■ , - - . Principles of X Ray and Radium Dosage by ALBERT BACHEM, PH. D. Illustrated with 70 engravings and 38 charts PUBLISHER ALBERT BACHEM, Ph. D. 502 Oakwood Boulevard CHICAGO COPYRIGHT, 1923 BY j ALBERT BACHEM, Ph. D. PREFACE Roentgen ray and radium therapy has passed over a long and rocky road. The first enthusiasm inspired by the results of surface therapy was succeeded in 1905 by a realization of the many harmful effects of the rays. As a consequence radiation therapy entered a period of depression from which it slowly emerged with the pre- vention of injury as its goal. Dosimeters were intro- duced, which enabled a determination of the intensity and of the quality of the rays and made a sure dosation possible. Innumerable single treatments led to treat- ment methods, which were more or less certain of suc- cess and avoided serious injuries. Deep therapy passed through similar stages. The use of very penetrating rays for the treatment of diseases which have their seat within the body produced results far beyond expectations. However, serious injuries soon appeared. At present therefore the general conviction is that caution must be observed; that existing methods must be subjected to thorough test and revision; and that formulae and methods must be developed, which increase the surety of the treatment. In the broadest sense we are dealing with the question of correct dosage. But both the problem of correct dosage as well as the cor- rect application of the dose are much more difficult here than in the case of surface therapy. Not only difficult measurements but difficult calculations must be made. To carry out a cross fire irradiation the entire treatment must be carefully planned in advance. For this a knowl- edge of the physical and of the biological action of hard 3 4 PRINCIPLES OF X RAY AND RADIUM DOSAGE rays is necessary; moreover, a knowledge of the methods of measuring, calculating and applying the radiation is required. The present volume is to contribute to this end; it treats of the most recent methods of practical dosage. It is assumed, that the reader is already familiar with the elementary principles of physics and of measuring technique; a discussion of fundamental concepts such as voltage and amperage, description of transformer and tube, as well as a discussion of the fundamental phenom- ena of radioactivity, has therefore been omitted. These subjects are so well known and have been so frequently and thoroughly discussed, that we shall merely give a few references. For the fundamental physical concepts we recom- mend the text books of physics in use at various high schools and colleges. For a discussion of electrical apparatus and phenomena within the tube we recommend the article by John K. Robertson in the Radiological Journal, 1923: “X-Rays and X-Ray Apparatus/’ For a study of radioactivity, N. E. Dorsey’s excellent book: “The Physics of Radioactivity” may be recommended. This volume deals chiefly with the following subjects: Chapters I and II treat of the exact definition and methods of measurement of both intensity and hardness. In Chapter III the distribution of the Roentgen and radium radiation in the tissues are discussed on the basis of the most recent physical investigations. In Chapter IV the problems of relative and absolute dosage are thoroughly discussed in the light of the latest developments. In Chapter V, finally, the most important doses likely to occur in practice are illustrated by a series of cases and PREFACE 5 treated from the standpoint of the most recent advances in deep therapy. It has been the author’s aim throughout the book to enable and encourage the reader to do his own thinking so that he can stand squarely on his own feet. Only in this way it is possible to discourage the strong tendency toward routine methods of treatment. In the opinion of the author one disadvantage of the available literature, especially of text books, is the fact that only radium therapy or only Roentgen therapy is treated; the two fields are never clearly differentiated, nor is the field where the two overlap, namely, combined Roentgen-Radium therapy, adequately covered. In the present volume particular attention has been paid to these points. If, however, Roentgen therapy has been given more space than radium therapy, it has been done for two reasons; first, because the calculation and application of Roentgen radiation is fraught with much greater diffi- culties than that of radium radiation; and second, because radium rays can be considered as special cases of Roent- gen rays and cathode rays and can therefore be con- veniently discussed with them. Furthermore, there is no occasion for again discussing a subject which has already been adequately treated in Dorsey’s excellent book: “The Physics of Radioactivity.” Besides drawing on his own experience and investiga- tions the author has gleaned a great deal of material from the literature—the German literature in particular since it was particularly easy for him and not so readily available to the reader as the Anglo-American literature. In the form of tables and curves the book contains a wealth of material useful in practice. Unfortunately, 6 PRINCIPLES OF X RAY AND RADIUM DOSAGE the isodosage charts could not be inserted in natural size. However, such charts can be obtained directly from the author. (See page 1.) The study of this volume shows that the character of X-Rays is as well known today as the character of light rays and Hertzien waves. The unknown quantity x is no longer present. Twenty-seven years ago their dis- coverer was justified in modestly calling them X-Rays; today we have reason for calling them Roentgen rays out of recognition and thankfulness to him. For this reason the author has given the latter term the preference. The author wishes to express his thanks to Mr. Alfred W. Simon for his translation of the manuscript into English and also to Dr. R. A. Ziehn for his assistance in the preparation of the biological portions of this work. TABLE OF CONTENTS Preface 3 Introduction: The production of radium and X rays 11 I. Determination and measurement of quantity 17 1. Intensity, energy, dose 17 2. Indirect methods of measurement 22 X ray energy as dependent on: Kilovoltage 23 Milliamperage 23 Transformer and rectifier. 24 X ray tube 27 Filtration 27 Focal skin distance 30 Size of field 32 Time of exposure 35 Radium energy as dependent on: Amount of radium 39 Concentration of radium 40 Filtration 42 Focal skin distance 46 Time of exposure 52 Radium needles 52 Radium capsules 55 Solution of radium and emanation 57 7 8 PRINCIPLES OF X RAY AND RADIUM DOSAGE 3. Direct methods of measurement based on: Thermal effects 59 Chemical effects 60 Photographic method 60 Selenium cell 64 Ionization of gases 66 Large chamber, electrostatic units 69 Electroscope 74 Iontoquantimeter 79 4. Biologic scale and methods of measurement.. . 83 Skin doses 84 II. Definition and measurement of quality 93 1. Wave length and spectrum of X rays and of gamma rays 94 Continuous and discontinuous spectrum.... 96 Effective wave length 109 2. Practical definitions of hardness 112 Percentage decrease per centimeter 117 Half value layer 117 Depth dose 117 Measurement of, with iontoquantimeter. 119 Absorption coefficient 121 Measurement of, with electroscope 122 Alpha and beta and gamma rays 123 III. Distribution of X rays and radium rays in various media 128 1. Laws of absorption and scattering 128 2. Laws of distribution 144 3. Distribution curves, distribution charts 153 Roentgen distribution charts 155 Radium distribution charts 164 Secondary rays 169 TABLE OF CONTENTS 9 4. Biologic facts regarding quality and intensity distribution 171 The error of hardness 172 Theories of biological action 173 * Biological differences between hard rays, soft rays, and corpuscular rays 179 IV. Practical dosage 181 1. Installation of Roentgen equipment 181 Tube holder 182 Tube box 185 Treatment couch 186 Half cylinder 187 Double tube installation 191 Protection against radiation 192 Prevention of radium sickness 192 2. Standardization of a Roentgen ray installation. 193 Choice of kilovoltage 194 Choice of milliamperage 197 Choice of filtration 197 Exposure time 198 Depth distribution 200 3. Periodic check of installation 202 4. Determination of the practical dosage 202 Surface dose 203 Dose at points within the body 207 Combined Roentgen ray and radium treat- ment 211 5. Determination of the total energy applied 215 6. Aids to practical dosage 218 Sensitizing of tissue 218 Desensitizing of tissue 220 Superposed layers 220 10 PRINCIPLES OF X RAY AND RADIUM DOSAGE V. Examples of treatment 222 1. Biologic facts underlying dosage 222 Stimulating doses 222 (blood diseases, metabolism, arthritis, gout, high blood pressure, ulcers of stomach, tuberculosis, lupus, etc.) Impairing doses 228 (leukemia, metropathia, myoma, osteo- malacia, carcinoma, sarcoma.) Lethal doses 241 2. Methods of treatment 244 Areas at the surface; method of Holzknecht; superficial diseases 245 Areas in the interior; methods of Seitz and Wintz; Hohlfelder; Warnekross-Dessauer; Juengling; diseases of uterus, ovaries, stomach, hypophysis, lungs, joints 250 Areas at intermediate depths; various meth- ods; diseases of vulva, axilla, larynx, etc. .. .265 General treatment 271 Gout, arthritis, etc.; general carcinoma- tosis, lymphosarcoma, etc. Complex cases 272 Combination of X rays and radium. Cancer of uterus, tongue, lips, etc. 3. Case record blank 273 INTRODUCTION The Production of Radium and Roentgen rays. The most important of the known radioactive ele- ments are radium and mesothorium. Radium, an alkali earth element, similar to barium, of atomic weight 226, is used chiefly in the form of its com- pounds as chloride, bromide (soluble), sulphate and car- bonate (insoluble). In decomposing it emits three types of radiation: alpha, beta and gamma rays. The alpha rays are positively charged helium nuclei thrown off by the disintegrating radium atoms. These nuclei have a relatively large mass, hence acquire a lower velocity and are less penetrating than the beta rays. The beta rays are negatively charged particles (elec- trons), which are projected with enormous velocities. The gamma rays are a wave motion in the ether very similar to light and Roentgen radiation and differ from these two only in wave length. The shortest known wave lengths and most penetrating rays occur among the hard gamma rays. Radium is produced in the course of time from ura- nium and the two are found in nature in definite pro- portions. To each gram of uranium there corresponds 0.333 micrograms of radium, that is 1/3 of a millionth of a gram. Radium decomposes so slowly that it requires some 1690 years for a given quantity to decay to one-half that quantity. This period is accordingly called the half decay period. The average life, that is the average value of the actual life of all radium atoms, amounts to 2440 years. 11 12 PRINCIPLES OF X RAY AND RADIUM DOSAGE The transformation products of radium are two gases, inactive helium and active radium emanation. The atomic weight of the latter is 222. Both radium and radium emanation send out only alpha rays, it is only the further products Radium A and Radium B, etc., which send out beta and gamma rays. The half decay of radium emanation is less than 4 days, 3.81 days to be exact, hence it disappears very rapidly if it is separated from the parent substance. If the emanation remains in con- tact with the parent substance as in a closed container, then a state of equilibrium is reached in about 30 days. It is only when this stage of equilibrium is attained that radium has the full alpha, beta and gamma activity. If the emanation is continually removed, the intensity of the radiation is reduced to a small fraction of its value at equilibrium. Mesothorium is a decomposition product of thorium, and decomposes with the production of beta and gamma rays into products which sent out alpha, beta and gamma rays. The half decay period of mesothorium is 6.7 years; its products also are short lived. Since the radia- tions of radium and mesothorium are not markedly dif- ferent, there is a possibility that a buyer may receive active preparations of mesothorium instead of the longer lived and more valuable radium. This will not be the case, however, if the radium is purchased from the lead- ing radium companies who issue a certificate guarantee- ing that the preparation contains only radium and not mesothorium. Radium and its salts are measured in grams, milli- grams, and micrograms of the element. The emanation is measured in curies, millicuries, and microcuries. One curie of emanation is the amount which is in equilibrium INTRODUCTION 13 with one gram of radium; 1 X 10~10 curies is called one eman. To determine the quantity of mesothorium, it is compared with radium; one gram of mesothorium is defined as the quantity which produces the same inten- sity of radiation as one gram of radium when both are filtered through 5 mm. of lead. Radium and other radioactive substances are widely distributed in nature. The best known radioactive ores are pitchblende and carnotite. Radioactive materials can be detected in small quantities in all earths and min- erals. The igneous rocks (crystalline slate, granite, etc.) contain about 3 X 10“12 grams of radium per gram of rock and 2.6 X 10—5 grams of thorium. In sedimentary rock radioactive elements occur in very different concen- trations. The greatest concentration is found in clays; the least in lime and sandstone. Nearly all springs, especially those which originate in eruptive strata, show a content of radium emanation, at times radium as well. Of the well known therapeutic springs, Oberschlema contains 21000 eman per liter or 2 microcuries per liter. The Wettinquelle Bad Brambach 8250 eman per liter or 0.8 microcuries per liter. Quarry water, Joachimstal, 2200 eman per liter or 0.2 microcuries per liter. Springs, Gastein, 1500-2000 eman per liter. Springs, Kreuznach and Karlsbad, 100-630 eman per liter. Springs, Wiesbaden, 80-240 eman per liter. Most springs and rivers contain traces, 1 to 10 emans. Ocean water is almost totally inactive. Also the atmosphere contains radium emanation, chiefly near the ground. This is due to two causes. First 14 PRINCIPLES OF X RAY AND RADIUM DOSAGE the radium emanation comes from the ground and sec- ond the emanation is much heavier than air and sinks to the lowest level. The greatest emanation content is found in caves; the air in the tunnel of the Porphyr Mountain at Kreuz- nach contains as much as 900 emans per liter. A very penetrating gamma radiation has been observed in the atmosphere especially at high altitudes. The distribution of this radiation would lead to the con- clusion that it is of cosmic origin. This radiation very likely originates from beta particles of high velocity, which are projected by the sun. On account of its radio- active content the air is ionized; the greatest concentra- tion of ions being found near the ground, in caves, as well as at high altitudes. From this viewpoint the administering of radium in small doses (radium-water, inhalation of emanation) is a very natural cure; it reestablishes conditions, which are excluded by our modern civilization. While primitive man was always in contact with radioactive materials by living in caves, sleeping on the ground, drinking from springs, etc., these things are entirely lacking in the household of civilized man. Very likely radioactive fac- tors are equally as important for the stimulation of meta- bolism and the prevention of a series of diseases as sun- shine and fresh air. For the production of Roentgen rays a great variety of electrical apparatus and tubes is available. The voltage between 140 K. V. and 230 K. V. used at present can be delivered by the following apparatus: (a) Static machines. On account of their low output they can only be used for experimental purposes, not for treatment. INTRODUCTION 15 (b) Induction coils. These were used chiefly with gas tubes during the development period of Roentgen technique. In Europe they are still widely used. (c) Alternating current transformers with rectifiers. These have found the widest application, especially in America. All discussions and measurements in this vol- ume refer to tubes which are operated in this way. (d) High voltage batteries. For experimental pur- poses for which a constant potential is required high voltage batteries are particularly suitable. They are used in a few laboratories in the United States. (e) Apparatus of Hull. An apparatus which is very promising is that devised by Hull and De Coudre; it con- sists of two thermionic vacuum tube rectifiers together with the proper inductances and capacities for rectifying the alternating current wave and reducing the fluctua- tions to less than 1 per cent. The gas tube is gradually disappearing from Roent- gen practice. The present volume is concerned only with radiation produced by Coolidge tubes; all measurements have been made with Coolidge tubes. While in the Coolidge tube the intensity of the radiation is controlled independently of the voltage by varying the temperature of the fila- ment and therefore the number of available electrons, in the Lilienfeld tube used in Europe the filament is always at the same temperature and is large enough to produce an excess of electrons, the number supplied to the anticathode being regulated by an auxiliary circuit. Recently Lilienfeld has introduced a new tube in which a point electrode is placed only a few millimeters away from the anticathode in an extremely high vacuum. On account of the high potential gradient, electrons are 16 PRINCIPLES OF X RAY AND RADIUM DOSAGE pulled out of the cathode and projected against the anti- cathode. These electrons carry the electric current and produce the Roentgen rays. The author is not of the opinion that this type of tube is very promising since the principle of the independent regulation of current and voltage is again abandoned in this design. The tube so far is useful only for diagnostic purposes and not for deep therapy. CHAPTER I Determination and Measurement of Quantity § 1. Intensity, Energy, Dose. Two important properties completely define a light ray physically, namely: intensity and color. A state- ment as to quantity and one as to quality are therefore necessary to characterize a light ray. The same holds for Roentgen rays and radium rays. The corresponding terms here are intensity and hardness. This chapter deals with the determination and meas- urement of intensity; the following one will be devoted to the determination and measurement of hardness. The intensity of radiation is the amount of energy which falls in unit time (1 second) on unit area of a sur- face (1 square cm.) perpendicular to the direction of propagation of the radiation. Therefore it is the energy density produced or applied during unit time. This magnitude is of importance technically because it is a direct measure of what might be called by analogy the (candle) power of the Roentgen ray (light) source. The value of a given Roentgen ray installation can thus be easily estimated by the intensity of radiation it emits. Of course, the hardness of the radiation must also be considered before a given machine can be completely characterized. A knowledge of the intensity of the radiation is further of great practical importance on account of the fact that the biologic reaction depends to a marked degree on the intensity and the time of radiation conjointly. The 17 18 PRINCIPLES OF X RAY AND RADIUM DOSAGE product of intensity and time of radiation is called the surface energy. This definition can be expressed by the simple equation: E = IXt (Surface energy = Intensity X Time) This equation states that the same surface energy can be applied in various ways: a small intensity can be applied for a long interval, or a large intensity can be applied for a short interval, to produce the same final result. If the product is the same in both cases, the same surface energy has been applied. The biologic effect, however, depends to a much greater degree on the amount of energy actually absorbed by the tissues than it does on the surface energy applied. It has been found universally true in physical science that only absorbed energy can be transformed into other forms of energy. Instances of this are: the production of heat, secondary electron emission, chemical dissocia- tion, etc. It is therefore reasonable to suppose that only absorbed energy can produce biologic reactions. It will be shown later that the soft rays are absorbed to a much greater degree than the hard rays. Hence the two kinds of rays will appear to produce very different physio- logical effects if they are compared in terms of surface energy. If, however, they are compared on the basis of absorbed energy, the dependence of the biologic effect on the hardness of the radiation is not so marked. It has been found that the general reaction of a patient to extensive radiation is governed by the total quantity of energy absorbed, and therefore transformed, in the interior of the body—other factors, such as the region treated, being the same. On the other hand, a local reac- tion, say of the skin or of cancer tissue, is determined DETERMINATION AND MEASUREMENT OF QUANTITY 15 primarily by the energy density applied. Very different results will be obtained when a small region of the skin is subjected to a high energy density than when a large surface is subjected to the same total energy but to a proportionately smaller energy density. In the latter case the energy absorbed per cubic centimeter governs the biologic reaction. The energy absorbed per cubic centimeter of tissue is called the volume energy or dose. If the distribution of energy in the interior of a given volume is not uniform, the volume may be thought of as divided into a number of thin strips at every point of which the absorbed energy is practically the same; and these strips may further be thought of as bounded in such a way that each of them encloses one cubic centi- meter of tissue. In this way the dose can also be defined for thin surface layers. To show the application of this idea let us consider the following problem: Required to determine whether a surface inclined at an acute angle to the direction of propagation of a Roent- gen ray beam receives the same or a smaller dose than a surface which is perpendicular to this direction. Let a beam of Roentgen rays (Figure 1-a) fall per- pendicularly on a surface layer and let the thickness of the layer be such that its volume is exactly one cubic centimeter. The dose within a layer depends on the energy which reaches the surface together with the dis- tance over which absorption can occur. The distance in this case is h and is equal to the thickness of the layer. Consider next the condition represented by Figure 1-b, in which the Roentgen ray beam strikes the surface of the layer obliquely. The same amount of energy is 20 PRINCIPLES OF X RAY AND RADIUM DOSAGE spread over a larger surface, the energy received per square centimeter is smaller in proportion. However, the path along which absorption takes place is greater in the same proportion (12) so that the dose which the layer receives is exactly the same as before. A smaller surface energy but greater absorption produce exactly the same Fig. 1. Perpendicular and Oblique Irradiation. dose when the beam strikes the surface layer obliquely as when it strikes perpendicularly. This conclusion is correct only for hard, penetrating rays for which it can be assumed that the energy absorbed at all points of the layer is approximately constant. For very soft rays such as those used in skin therapy the above conclusion does not hold; with these rays the dose decreases as the angle between the path of the rays and the plane of the surface decreases. It is notable in this connection that several of the DETERMINATION AND MEASUREMENT OF QUANTITY 21 recent books on high voltage therapy give an incorrect formula for the dose produced by an oblique beam. The correctness of the conclusion drawn above may easily be subjected to the test of biological and physical experiments. A film bent into a cylinder is struck at all angles from zero degrees to ninety degrees when exposed to a Roentgen ray beam, but shows uniform optical density1 on being developed. The position of a film rela- tive to the direction of the beam cannot be deduced by an inspection of its optical density. According to the formula given in several books, the intensity ought to assume all values from a maximum down to zero, the latter occurring in the regions of grazing incidence. When the buttocks are rayed the skin surfaces inclined towards the sagittal plane show an equal or even greater erythema than the surrounding regions; according to this formula they should show a much milder erythema on account of the inclination of their surface to the path of the rays. As a matter of fact, it is found that the scattered radiation comes into play and actually produces a somewhat greater erythema on these surfaces than occurs elsewhere. In the following we shall take up in detail methods of measuring the intensity and the energy of a beam of rays. Each such method is based on the trans- formation of absorbed energy and this, in turn, depends on the hardness as well as the intensity of the radiation. For the sake of simplicity the effect of hardness will be ignored in this chapter but any uncertainties introduced in this way will be cleared up in a later chapter. 1 Optical density is a measure of the degree of black- ening or opacity of the film. 22 PRINCIPLES OF X RAY AND RADIUM DOSAGE § 2. Indirect methods of measurement. The methods, which are used for the estimation or measurement of the energy of Roentgen rays or radium rays, can be classed as direct and indirect methods. An indirect method measures the primary conditions which govern the production of the radiation and endeav- ors to deduce the energy from these conditions. The factors, which determine the energy applied to a point at the surface of the skin are: 1. Kilovoltage. 2. Milliamperage. 3. Transformer and type of rectifier. 4. Roentgen ray tube. 5. Filters. 6. Focal skin distance. 7. Size of field. 8. Time of exposure. On account of the large number of variable factors an accurate determination of the radiated energy is pos- sible only if most of the factors are held constant. The usual and widespread custom of speaking in terms of milliampere minutes is justifiable only when the other factors enumerated above are kept constant. The state- ment that 600 milliampere minutes produce an erythema usually assumes the following conditions: 1. 200 kilovolts (peak value). 3 and 4. A commercial transformer, full wave rectifi- cation, Coolidge tube. 5. 1 millimeter of copper plus 1 millimeter of alum- inum. 6. 50 cm focus skin distance. 7. Approximately (20 cm)2 size of field. 2 and 8. 600 milliampere minutes, say five milliam- DETERMINATION AND MEASUREMENT OF QUANTITY 23 peres for two hours or six milliamperes for 100 minutes. Should any one of these factors be radically different from the above, the applied energy cannot be deduced from the measured milliampere minutes without some further calculations. In such cases the amount of applied energy can be deduced by the use of certain more or less familiar physical principles. This will be illustrated by the following examples: Ex. 1. 180 kilovolts instead of 200 kilovolts are used. The intensity of strongly filtered rays is approxi- mately proportional to the square of the kilovoltage. The calculation is best carried out in terms of percent- ages, taking into account the fact that if two numbers differ from each other by a small percentage, their squares differ from each other by double this percentage. As an illustration consider the numbers 90 and 100; 90 differs from 100 by 10%. The square of 90, 8100, differs from the square of 100, or 10000, by 19% or roughly, 20%, which is double 10%. Again 105 is 5% greater than 100; its square, 11025 is approximately 10% greater than the square of 100 or 10000. This holds approximately up to plus or minus 20%. Returning to our problem, 180 kilovolts is 10% less than 200 kilovolts. The intensity of the radiation is therefore diminished; that is to say, with the same num- ber of milliampere minutes 80% of the required energy is applied. Hence 25% more milliampere minutes or 750 milliampere minutes produce the same reaction with 180 kilovolts as 600 milliampeters produce with 200 kilovolts. Ex. 2. The milliamperage is to be decreased from 5 milli- amperes to 4 milliamperes. As a first approximation, it is necessary to increase the time in the inverse ratio of the milliamperage. 24 PRINCIPLES OF X RAY AND RADIUM DOSAGE In some cases where the milliamperages are widely different, radical departures from this rule are noted. For every milliamperage there is a best setting of the rectifier. If the correct adjustment has been made for 5 milliamperes then the output at 8 milliamperes will be less than would correspond to the ratio 8:5. It may per- haps be nearer in the ratio of 7.5 : 5. Conversely, if the rectifier has been set for maximum efficiency at 8 milliam- peres, then the intensity may decrease in the ratio of 4.7: 8 when the milliamperage is changed from 8 to 5 milliamperes. Two tube operation and single tube opera- tion are sometimes very different since the two tube operation corresponds to double milliamperage. Some installations will work best with two tubes, others with a single tube. When a machine is calibrated, the calibra- tion should be made in terms of the conditions most likely to be used in practice. With some transformers and rectifiers two and three tube operation is inferior to single tube operation so that increasing the number of tubes does not increase the output in proportion to the number of tubes. Ex. 3. From the output of one installation the output of a second installation is to be deduced. The same oper- ating conditions are assumed. The wave form of two installations can be so different, that the radiation intensities vary as greatly as from 1 to 6. An installation which maintains constant poten- tial across the tube can produce about three times as much hard radiation as an ordinary installation consist- ing of a good transformer with a mechanical rectifier. When light filtration is used, the transformer-rectifier installation does not compare so unfavorably with the constant potential apparatus as regards intensity, but in DETERMINATION AND MEASUREMENT OF QUANTITY 25 this case the difference in hardness is more pronounced and is in favor of the constant potential apparatus. Two constant potential installations do not differ in output since all factors including the wave forms are the same. However, the various transformers found on the market are very unlike in many respects, due to the various wave forms caused by various constructions in transformers (i. e., magnetic leakage, autocontrol or rheostat con- trol) and peculiar rectifying designs, all of which tend to change the characteristics of the wave form and the phase relationship. In some installations high voltage surges occur, which in some cases are so strengthened by electrical resonance. These surges can so influence a sphere gap measurement, that an accurate determination of the kilovoltage becomes impossible. Single, thin sparks, which often jump much farther, than the anticipated gap, are proofs of the pres- ence of these high tension surges and indicate that the sphere gap measurement is unreliable. These surges do not influence the output of a tube but by rendering the sphere gap measurement uncertain they may indirectly cause differences in the intensity of the radiation. Two types of rectification are in common use. The first applies only one-half of the alternating wave to any one tube and either applies the other half to a second tube or wastes it altogether if only one tube is used. This type is called single wave rectification. The second type rectifies both halves of the wave and applies them to a single tube, or to two tubes connected in parallel. Theoretically, there should be no great difference in efficiency between single and full wave rectification. A current of 5 milliamperes through the tube means an average value of 5 milliamperes. In the case of single 26 PRINCIPLES OF X RAY AND RADIUM DOSAGE wave rectification an average value of 5 milliamperes is produced by pulses of high peak value, with periods of no current transmission between; in the case of full wave rectification the peak values are much lower but the num- ber of pulses occurring per second are doubled. In the first case, the peak value may be 12 milliamperes but the current flows only half of the time; in the second case the peak value may be about 6 milliamperes and the cur- rent flows practically all of the time. Nevertheless, it is found that the two types do differ in efficiency by about 10%. This is due to the fact that the intensity does not increase in direct proportion to the millamperage. When the peak milliamperage is high, the wave form is not so favorable; the efficiency is improved if the current flow is distributed over a longer period. It has been observed that the maximum safe milliamperage with single wave rectification is lower than with full wave rectification. If the safe limit is exceeded, the milliamperage suddenly increases, and equilibrium can only be attained again by cutting down the filament current. Another factor to be taken into account in consider- ing the production of the Roentgen rays is the magnitude of the rectifier arc (the mechanical arc). As the rectifier arc is increased, the soft radiation component is increased. Conversely, however, no matter how small the arc is made, the soft ray component cannot be reduced to zero. The larger the rectifier arc, the smaller will be the tend- ency for sparking to occur and therefore the smaller will be the danger of high tension surges. The best setting of the rectifier is attained when only a mild spark occurs at the make; arcing at the break should be avoided as it results in a very unsteady opera- tion of the tube and shortens its life. DETERMINATION AND MEASUREMENT OF QUANTITY 27 Ex. 4. How do new and used Coolidge tubes or well evacuated and poorly evacuated Coolidge tubes differ in the production of Roentgen rays? The chief advantage of the Coolidge tube over the gas tube is that both intensity and hardness can be held constant. However, in comparing various Coolidge tubes or even the same tube with itself after a long period of operation, first order differences will be detected in intensity. Differences in hardness with the heavy filtra- tion used in deep therapy are always of the second order. Well evacuated tubes give such consistent results, that no differences can be detected even with the most sensitive measuring instruments. Poorly evacuated, fluorescent tubes, which periodically give off gas, and tubes which can be held at a constant milliamperage only by special efforts, may show considerable variation from the normal intensity and in exceptional cases may go as much as thirty per cent below the normal intensity. Even good tubes, which have been in service for a long period finally show a diminished intensity; this is caused by the pitting of the target and a greater partial absorption of the rays emanating from it as well as by selective absorp- tion of the rays by the tungsten deposit on the walls of the tube. After 500 hours of operation the intensity has been decreased 10 to 15%; in one case of more than 1000 hours of operation the intensity was 23% below normal. Accordingly, the time of exposure must be increased 10 to 20% to achieve the same results as with new tubes. Ex. 5. Yz millimeter of copper and 24 millimeter of cop- per instead of 1 millimeter of copper are used. The intensity is not a simple function of the filtration. The effect of the filter depends largely on the composi- tion of the beam, that is on the relative amounts of hard 28 PRINCIPLES OF X RAY AND RADIUM DOSAGE and soft rays. The composition of the beam in turn varies greatly with operating conditions and depends in particular on the transformer and rectifier used. Hence, only a few special cases can be treated and it must be understood that the data given below is not valid for the general case. At 200 K V the intensity changes approximately 23% on passing from 1 millimeter of copper to 24 millimeter of copper; and 60%, on passing from 1 millimeter to millimeter of copper. At 150 K V the differences are more marked. On passing from 1 millimeter to 24 milli- meter the intensity changes 26%. On passing from 1 millimeter to millimeter the intensity changes 74%. As a rough approximation the following rule can be given for the two kilovoltages under consideration: In changing from 1 millimeter to 24 millimeter the intensity changes 25% or 24- In changing from 1 millimeter to 24 millimeter the intensity changes 67% or 2/3. The corresponding treatment times are calculated as follows: If the intensity is increased by 24 or in the ratio of 4:5, the treatment time must be cut down in the inverse ratio, namely 5 :4, that is, the time must be decreased by 1/5. In the second case the intensity is increased by 2/3 or in the ratio of 3 : 5. The time must be cut down in the ratio of 5 : 3, that is, the time must be decreased by 2/5. In Fig. 2 the results of physical and biologic measure- ments are given graphically in a series of curves. The figure shows the intensity as a function of kilovoltage and thickness of filter. The intensity at 200 K V, and 4/4 millimeters of copper is arbitrarily taken as 100. The ordinates represent intensities; the abscissae DETERMINATION AND MEASUREMENT OF QUANTITY 29 Intensity Intensity as a Function of Kilovoltage for Various Filters. Ktf 2 Time (Minutes) IUU Tig: 3 Erythema Time as a Function of Kilovoltage for Various Filters. 30 PRINCIPLES OF X RAY AND RADIUM DOSAGE voltages; each curve represents a certain filter thickness. Kilovoltages are compared by running along any curve; filters by passing from one curve to another. If the intensity corresponding to one kilovoltage and one filter thickness is known, then this series of curves makes it possible to deduce the intensity corresponding to any other voltage and any other filter thickness. The curves in Fig. 3 are of still greater importance. These show the time of radiation as a function of the kilovoltage and the filter thickness. For simplicity the time corresponding to 200 K V and 1 millimeter of cop- per is put equal to 100. The change in treatment time expressed in per cent can be read off directly from these curves for any change in kilovoltage or filter thickness. A similar series of measurements has been carried out by Fallia and Quimby with 140 K V and various thick- nesses of brass and aluminum filters. The results were as follows: Percentage of radiation transmitted Brass filtration Aluminum filtration Ratio Aluminum Brass 100 % 0 mm 0 mm 25.6 % .15 mm 4 mm 26.6 22.2 % .20 mm 5 mm 25.0 19.5 % .25 mm 6 mm 24.0 16.0 % .34 mm 8 mm 23.0 13.5 % .43 mm 10 mm 23.2 11.8% .53 mm 12 mm 22.6 9.0% .77 mm 16 mm 21.8 7.1 % 1.05 mm 20 mm 19.1 Ex. 6. The focus skin distance is increased from 50 to 60 centimeters. DETERMINATION AND MEASUREMENT O'F QUANTITY 31 The physical law which applies to this case is as fol- lows: The intensity is inversely proportional to the square of the distance. If the distances are in the ratio of 50 : 60, or 5 : 6, which is the same thing, then the corresponding intensities are in the ratio of 36 : 25. If the intensity at 50 centimeters be taken as 100, which again is a convenient figure for calculating in terms of percentages and if, further, the intensity at 60 centimeters be taken as X, we have the equation 100 :X — 36: 25 from which X = 2500 : 36 = 69.5 The intensity at 60 centimeters is therefore about 70% of that at 50 centimeters. It is easier to determine the ratio of the corresponding treatment times directly. The exposure times vary inversely as the ratio of the intensities: a smaller intensity means a longer exposure. The law of inverse squares can be restated: The treatment time varies directly as the square of the focus skin distance. If as before we take the time corresponding to 50 centimeters equal to 100 and call the unknown time t, we have the equation t: 100 - 36: 25 therefore t_3600_ 14^ The time of radiation must therefore be increased 44% if the focus skin distance is changed from 50 centi- meters to 60 centimeters. The same holds for the milli- ampere-minutes: instead of 600 milliampere-minutes, 864 milliampere-minutes must be applied. A question of practical importance is what a small 32 PRINCIPLES OF X RAY AND RADIUM DOSAGE error in the focus skin distance makes in the intensity. For this calculation we shall apply the principle we have used once before, namely, if two numbers differ by a small percentage, then their squares differ by double this percentage. Suppose we make an error of 2x/2 centimeters (1 inch) in making the 50 centimeter setting. This is an error of 5%; the time of radiation will then be in error by double this amount of 10%. If the error is made in the sense that too large a focal distance is used, it would mean that the time of exposure needs to be increased by 10%. Unless this is done the region treated is slightly under- exposed. If the error is made in the opposite direction, then the region treated is slightly overexposed. An error of plus or minus 10% can hardly be detected biologically and is therefore not of great importance. However, an accidental error of 5 centimeters (10%) in the setting would mean an intensity difference of 20% and this represents a dosage error which would very likely make itself manifest by its consequences. In the literature the question of whether the law of inverse squares is rigorously true has often been raised. This question will be answered in the following example dealing with the scattering of the Roentgen rays. It may be here answered, that for all practical biological purposes the law of inverse squares is valid. Ex. 7. The size of the field is to be changed from (20 cm)2 to a smaller value. How will this effect the dosage? The energy radiated to a surface layer of a body con- sists of two components: the primary radiation coming directly from the source of the rays and the secondary radiation scattered back by the interior of the body. The latter component depends on the volume traversed by DETERMINATION AND MEASUREMENT OF QUANTITY 33 the radiation. The greater this volume, the greater is the energy which is scattered back. With hard rays and a port of entry of 20 cm X 20 cm—a relatively large field—about 50% of the incident energy is scattered back. The following experiment shows this very clearly: An instrument which measures both secondary and primary radiation—for best results a small ionization chamber of a type which will be discussed in detail later —is put in the path of the direct beam, first without any absorbing or scattering bodies in the neighborhood, and second, with a large water phantom, preferably a cube 25 cm on a side, placed underneath. Figure 4. 4-. Effect of Scattered Radiation. The ionization chamber in the latter case should be half immersed in the water. If in the first case the inten- sity is found to be 100 then in the second case it will be approximately 150—the increase being due entirely to 34 PRINCIPLES OF X RAY AND RADIUM DOSAGE energy which is scattered back by the water within the cube. The amount of scattered radiation depends to a high degree on the volume which is being traversed by the radiation. If a narrow beam is sent into the water, then only a small volume can radiate secondary rays back to the surface. Then primary energy alone is pres- ent at the surface. Exact measurements show the fol- lowing relation between the intensity and the size of the field; the intensity for a field 20 cm X 20 cm is taken equal to 100. The following table gives the various inten- sities together with the corresponding times which are necessary in order to produce the same biological reac- tion. The last column gives, in addition, the milliampere- minutes under normal operating conditions. Size of Field Intensity Time Energy 20 X 20 cm2 100% 100% 600 M A min 15 X 15 cm2 95% 105% 630 M A min 10 X 10 cm2 87% 115% 690 M A min 5x5 cm2 77% 130% 780 M A min For fields greater than 20 cm X 20 cm the intensity is not appreciably greater; with a field of 20 cm X 20 cm the scattered component attains a practical maximum. On account of the addition of the scattered compo- nent, the inverse square law is somewhat modified when large volumes are rayed. The energy in the interior is increased by an increase in focus skin distance as well as by an increase in size of field. Since part of this energy is returned to the surface, the latter also receives a larger supply of energy. If the focus skin distance is changed from 30 centimeters to 60 centimeters the intensity at the surface ought to decrease to % of its value at 30 centi- DETERMINATION AND MEASUREMENT OF QUANTITY 35 meters. It is found, however, that due to the more favor- able distribution at 60 centimeters, a larger intensity is scattered back to the surface than was the case for 30 centimeters and the intensity at 60 centimeters does not fall in Y its value at 30 centimeters. According to measurements made by the author the intensity falls to 27% rather than to 25%. However, the deviation from the inverse square law is so small that in practice it is of little importance. Ex. 8. With apparently normal conditions, for some rea- son or other, say on account of a poor transformer, a low kilovoltage, a low milliamperage, let the intensity be low and the time of radiation too lengthy. The time of radiation is to be decreased from say 180 minutes to a more favorable time. Which factor is to be changed to obtain a shorter exposure time? (a) It is often possible to increase the kilovoltage from 200 to 210 or 215 K V without danger to the tube. This can be done in the following special cases: Limited capacity transformer. Single wave rectification. Absence of surges. Care must be taken that the tube does not fluoresce too brilliantly, that it does not crackle, and that the mil- liammeter does not show spasmodic increases in current. All these phenomena are indications that the danger point has been reached and that the kilovoltage is too high. (b) Often the milliamperage can be increased, for example, in the following cases: When the kilovoltage is low, which may occur in regions of low barometric pressure like Denver, Colorado Springs, Pueblo; when transformers of low efficiency 36 PRINCIPLES OF X RAY AND RADIUM DOSAGE [not, however, when used with single wave rectification] are employed; when the new tubes designated “200 K V, 8 milliamperes” are used; and when the tube is well cooled by an air blast from a blower or suction pump. Care must be taken that the tube does not overheat, that the anticathode does not bend and that gas is not given off. The presence of gas is indicated by a hissing sound, by an increase in milliamperage and a decrease of kilovoltage. (c) Sometimes the rectification can be improved. (d) Occasionally, the cause for low intensity is a tube which has been used too long or has developed gas. (e) In many cases the thickness of the filter is incor- rect. Some copper filters, which are stamped “1 milli- meter” actually have a thickness of 1.2 millimeters. If the patient is treated from below (on a couch), a mattress, a sheet, or even a wooden board is often interposed. All these substances show appreciable absorption. Mat- tresses frequently absorb 10 or 12%; a layer of wood equally as much. The time of exposure is accordingly unduly increased. These conditions can be remedied in the following ways: A smaller copper filter, perhaps or 34 millimeters of copper, can be used on account of the fact that the other substances also act as filters; the aluminum filter can be omitted since the characteristic rays from the cop- per are absorbed by the substances placed over it. Balsa wood, which absorbs about 1/10 as much as any other wood and still has sufficient mechanical strength even in 2 cm. thicknesses can be used. An air cushion also can be inserted into an aperture made in the mattress. By the use of one or more of these devices, the expos- ure time can be considerably shortened. From the laws DETERMINATION AND MEASUREMENT OF QUANTITY 37 and illustrations already given, an estimation of the new radiation time can be made. (f) In very unfavorable cases when none of the above remedies can be applied, the focus skin distance can be decreased. In this way the exposure time can be greatly shortened; but the distribution of dosage in the interior of the body is not so favorable as will be shown later. (g) An increase in size of field is not of practical importance for increasing the surface intensity, but it can be used to attain a better depth distribution as will be shown later. By a correct combination of these various factors the exposure time can be made fairly agreeable to the patient even in very unfavorable cases. The preceding detailed discussion of the many factors which influence the mil- liamperage shows that an estimation of the energy which a patient receives is possible by the indirect method only if all the various factors are accurately known. This usually is not the case when two Roentgen ray installations are to be compared. Apparatus and condi- tions of operation are so widely different in practice that a milliampere minute measurement is absolutely worth- less. A few examples will serve to illustrate this. (1) With apparently normal conditions 200 K V, 1 millimeter of copper plus 1 millimeter of aluminum, 50 cm. focus skin distance, 720 milliampere minutes did not produce an erythema. Careful measurements showed that the kilovoltage was only apparently 200 K V due to high voltage surges, which were produced by a poor 38 PRINCIPLES OF X RAY AND RADIUM DOSAGE adjustment of the rectifier with attendant sparking. An adjustment of the rectifier followed by a boosting of the kilovoltage produced the correct intensity, so that an erythema was produced by 600 milliampere minutes. (2) In one hospital it was found that 720 milliam- peres (occasionally 900 milliamperes) could be applied without producing a heavy erythema. The question of how this could be possible was asked of the author many times. Therefore careful measurements of the conditions were made. The results were as follows: (a) With really normal operating conditions, the apparatus was 12% below normal. (b) The voltage actually used was only 193 K V. (c) A thick, leather sheet was inserted, which absorbed 13%. The intensity under these operating conditions was therefore 28% below normal. Nine hundred milliampere minutes really corresponded to 650 milliampere minutes and was not really out of the ordinary. These examples show that it is erroneous to apply the milliampere min- utes used by one installation without further thought to another installation. A factor of safety of 20% should always be used in the beginning until the erythema dose has definitely been measured. On the other hand, the milliampere minute value is very useful in the operation of one and the same installation after the operating conditions are known and as long as they are kept constant or varied according to well known laws. The application of low, normal, or high energies measured out in terms of milliampere min- utes is a convenient and sure method of dosage. DETERMINATION AND MEASUREMENT OF QUANTITY 39 If, in addition to the other factors, the milliamperage is not changed, it is possible to use the simple method of treating with the time clock—a mechanical and accurate method of dosage. The indirect method of dosage is more favorable in the case of radium therapy than it is with Roentgen rays. The great advantage in the case of radium radia- tion lies in the constancy of the source. The intensity depends on fewer and more readily measured quantities. The latter are: 1. The amount of radium in milligrams. 2. The time. 3. The concentration. 4. The filtration. 5. The focus skin distance. The factors 1, 3, 4, and 5 determine directly the inten- sity of the radiation; the time factor determines the total quantity of energy applied. Milligram hours in radium therapy correspond to the milliampere minutes in Roent- gen therapy. The following should be observed in con- nection with the factors enumerated. (1) The quantity of radium: the number of milli- grams of the element. For the sake of standardization and ready comparison calculations should not be made in terms of radium bro- mide, radium chloride, radium sulphate, radium carbon- ate, etc., but in terms of the quantity of the element pres- ent in these compounds. The following factors can be used for this calculation: 40 PRINCIPLES OF X RAY AND RADIUM DOSAGE 1 mg Ra Cla — 0.761 mg Ra element 1 mg Ra Br2 = 0.585 mg Ra element 1 mg Ra Br2 + 2HaO = 0.536 mg Ra element 1 mg Ra SO4 = 0.702 mg Ra element 1 mg Ra C03 = 0.790 mg Ra element (2) The time is given in hours. The product of milligrams of radium element and time determines the energy applied to the tissues. It must be added in this connection that observations made by some German and American scientists indicate that the biologic effect is not entirely independent of the separate factors: milligrams of radium and hours of exposure. We shall come back to this subject in a later chapter; for the present it may be stated that for the quantities and times ordinarily used no very serious errors are made by assuming that the biologic reaction depends only on the product of the two. (3) It often happens that the concentration of the radium rays is ignored. The importance of this quan- tity may now be made clear. Let us consider two cases: Case 1. A surface is treated with one 25 milligram capsule for 10 hours. A certain reaction will result. Case 2. Two 25 milligram capsules are placed parallel a short distance apart in the same region as above and the same total number of milligram hours is given—that is, the treatment is continued for 5 hours. In this case the biologic effect will be approximately half of what it was in the first case although the same number of milli- gram hours have been applied. The amount, however, has in the second case been applied to two practically DETERMINATION AND MEASUREMENT OF QUANTITY 41 separate areas. In order to produce the same reaction as with the single capsule the number of milligram hours must be nearly doubled. Only after the milligram hours have been doubled will each region show' the same bio- logic effect. It is therefore misleading to state the total number of milligram hours unless the number of areas treated is also given. In other words, the number of milligram hours per unit of surface treated, namely the concentration of energy, is the primary factor. Plainly, we are concerned here chiefly with the reac- tion of the surface layers; at a depth of 5 cm. the energies do add in the expected way and the dosage at a depth of 5 cm. is the same in both of the cases cited above. This distribution of the energy over the surface layers is similar in the principles to the multiple field method of Roentgen ray therapy. By this method a favorable intensity is produced at a considerable depth without overexposing the surface layers. Acting on this idea Wilhelm Stenstrom has devised an apparatus which, pro- vided a sufficient number of radium preparations are available, makes it possible to produce an intensity at a depth of a few centimeters greater than the intensity at any point of the skin. In treating with several radium needles each single needle determines the intensity in its immediate neigh- borhood; a short distance away, however, the effects of the various needles overlap and add; and a stronger reac- tion is produced by the use of a number of needles with a proportionately larger number of milligram hours. The magnitude and distribution of the energy result- ing in such cases will be taken up in detail later. 42 PRINCIPLES OF X RAY AND RADIUM DOSAGE The effect of the concentration is very noticeable when superficial regions are treated with radium plaques. For example, if three plaques of different sizes: 1, 2, 4 centimeters square but with the same number of milli- grams of radium are applied for equal lengths of time, the biologic effects will be in the ratio of 4 : 2 : 1. In the first case, that of the smallest field, the same intensity is concentrated on a smaller surface than in the second and third cases. The terms double strength, full strength, and half strength may be used. If the same effect is to be produced in all three cases, the exposure times must vary as 1:2:4; or, with equal exposure times, the con- centration (not the total quantity of radium) must be kept the same. That is: the three plaques must have full strength: The 1 square centimeter plaque — 5 milligrams, The 2 square centimeter plaques—10 milligrams, The 4 square centimeter plaques—20 milligrams. Then each square centimeter will receive the radia- tion emanating from 5 milligrams of radium and, if the exposure time is the same, will receive the same quantity of energy. This, of course, is not rigorously true for the reason that the phenomenon of scattering comes into play much as it does with large ports of entry in the case of Roentgen rays. Since, however, as will be shown later, the intensity decreases very rapidly with the dis- tance when radium is used for treating surface lesions, the quantity of scattered energy is not very large. The effect of the size of the field is not so important with radium rays. (4) The filtration. The intensity of the radium radiation depends to a high degree on the filtration used. This is due to the DETERMINATION AND MEASUREMENT OF QUANTITY 43 fact that the radiation is composed of very different hard rays and that the soft components make up a large part of the total energy. The intensities of the alpha, beta and gamma rays, measured biologically, vary approximately in the ratio of 10,000 : 100: 1. The alpha rays usually are absorbed before they reach the tissues and therefore are of minor importance. The beta rays are the active component in the case of unfiltered or lightly filtered preparations and produce strong biologic effects. The gamma rays alone remain if heavy filtration is used but in comparison with the beta rays their biologic action is very mild. The following example shows the dependence of the erythema exposure time on the filtration. Ten milligrams of radium element placed in a radium needle of non-corrosive steel produce a definite erythema in 20 minutes, if the needle is placed directly on the skin. In this case part of the beta rays are effective. If the same preparation is filtered through iy2 millimeters of brass so that the beta rays are absorbed, 2 hours are necessary to produce the same reaction. If the contents of the needle were placed without filtration directly on the skin, 2 minutes would be sufficient to produce an erythema. The effect of the filtration on the intensity of radium radiation has been investigated very thoroughly by Failla and his coworkers: Quimby and Dean. The intensities were measured biologically; the experiments therefore are analogous to those made by Failla and by the author on Roentgen radiation. If the intensity of an unfiltered preparation (say a 44 PRINCIPLES OF X RAY AND RADIUM DOSAGE small glass tube containing radium emanation) is taken as unity, the following numbers indicate the intensities obtained with various thicknesses of brass filters, all other factors remaining the same: Brass Rubber Intensity 0 mm 0 mm 1.00 0.1 mm 1.2 mm 0.62 0.2 mm 1.2 mm 0.26 0.3 mm 1.2 mm 0.085 0.4 mm 1.2 mm 0.050 0.5 mm 1.2 mm 0.030 0.6 mm 1.2 mm 0.021 0.8 mm 2.4 mm 0.0145 1.00 mm 2.4 mm 0.0119 1.25 mm 2.4 mm 0.0105 1.50 mm 2.4 mm . 0.0098 1.75 mm 2.4 mm 0.0094 2.00 mm 2.4 mm 0.0090 Figure 5 shows these relations graphically. From the intensity corresponding to any one brass filtration, the Intensity Intensity Effect of Filtration on Intensity of Radium Rays. Pig: 5 mm trass filter DETERMINATION AND MEASUREMENT OF QUANTITY 45 intensity corresponding to any other can be deduced by comparing the indicated values. The curve shows the relatively strong filter action of thin glass, which ab- sorbs a large fraction of the alpha, beta and soft gamma rays. Beyond 1.5 mm of brass only a very slight change in intensity is observed on account of the extreme pene- tration of the residual gamma rays. The equivalence of various filter materials has been investigated by Quimby, again with reference to the biologic effect. The following table gives the results for aluminum, brass and lead in equivalent millimeters: Aluminum Brass Lead 0.60 mm 0.16 mm 0.08 mm 1.20 mm 0.32 mm 0.16 mm 1.74 mm 0.48 mm 0.25 mm 3.34 mm 0.96 mm 0.58 mm 6.11 mm 1.92 mm 1.10 mm 10.78 mm 3.04 mm 1.33 mm The values given by Friedrich and Kroenig do not agree very closely with those of Quimby, due probably to differences in the methods of measurement; accord- ing to the former 9.5 mm aluminum 1.5 mm brass .8 mm lead are equivalent. With the help of these relations it is easy to change from one material to the other. Silver filters a little more strongly than brass but the differences are neg- ligible. The substance used for radium needles, namely non corrosive steel, is an alloy which behaves very similiar to brass. 46 PRINCIPLES OF X RAY AND RADIUM DOSAGE (5) The same law of distance holds for radium rays as for Roentgen rays. The intensity varies inversely as the square of the distance. One important difference, however, must be noted. With a Roentgen ray tube the focus skin distance is always so large in comparison with the dimensions of the focal region that the law of inverse squares holds very exactly. In dealing with radium rays, the focal distances are of the order of a few millimeters (occa- sionally a few centimeters); hence we can no longer treat the preparation as a point source. The radiation reaching any given point is the sum of the radiations emanating from a series of points to each of which there corresponds a different focal distance. We can no longer speak of a single focal distance since this is not uniform. Thus the law of inverse squares cannot be directly applied. For a point on the skin adjacent to the preparation the intensity is smaller than would corre- spond to the law of inverse squares. The actual relation between intensity and distance can be calculated from the geometrical shape of the preparation; it has, more- over, been determined experimentally for most prepara- tions and arrangements used in practice. The greatest number of observations were made by Quimby. The values obtained have reference to an average erythema: “a very low reaction defined as the erythema produced on the skin of the average patient by a dose of 7.5 me hrs of ungltered radiation, applied at a distance of 2 cm. By unfiltered radiation is meant the radiation from the emanation in the capillary glass tube with no additional covering.” The accompanying tables are extracts from the wealth of data obtained by Quimby, except that the No filter 0.16mm brass + 1.2mm rubber 0. 35 mm alloy + rbbr. 0.5mm brass + 1.2mm rubber 1 mm brass + rbbr. 1.5 mm brass + rbbr. 2mm brass + 2.4mm rubber Emana- tion Tube Square Tube Square -euV4-£5 - ~7niZkSi, eZoudj Q&ssy\CstsiAsOcsj/vt* — Fig. 11. Diagram of Ionisation Chamber. If there is no Roentgen radiation, no current flows since the gas consists only of neutral molecules and is not conducting. If, however, a beam of Roentgen rays passes through the gas, the latter is ionized. On account of the attractions and repulsions exerted by the charged plates on the ions, the latter drift to the plates and in this way serve as carriers of electricity. They neutralize part of the charge on the plates; and a current flows from the source of E. M. F. to balance this loss. The galvanometer will therefore show a deflection. If the potential differ- ence between the plates is small, the ions travel with a low velocity and only a few reach the plates and give up 68 PRINCIPLES OF X RAY AND RADIUM DOSAGE their charge, most of them recombine on the way. If the applied potential difference is increased, the velocity of the ions becomes greater on account of the increased attraction and repulsion. Consequently fewer ions recombine, more of them reach the plates, and serve as electric carriers, hence the current increases. It increases in proportion to the potential difference, and Ohm’s law therefore applies also to the conduction of electricity through gases under these conditions. Of course, if the potential difference is further increased, a point is reached when all the ions formed are utilized to carry the current, then further increase in volt- age does not produce an increase in current. This cur- rent which is independent of the voltage is called the saturation current. If now the intensity of the radiation is increased, the current again increases, moreover it increases directly as the intensity of the radiation. The saturation current is therefore independent of the applied voltage but varies directly as the intensity of the radia- CltAsu/ztesijL Vo If /z. Characteristic Curve of Gaseous Conduction. DETERMINATION AND MEASUREMENT OF QUANTITY 69 tion. However, if the voltage is greatly increased, another phenomenon appears: the velocity of the ions becomes so great, that new ions are formed by collision with neutral molecules. In this way myriads of new posi- tive and negative ions are formed and. the current rises very rapidly. This phenomenon is called ionization by collision. Figure 12 shows graphically the variation of the current with the potential difference: (1) is the range in which Ohm’s law applies; (2) that in which saturation current is reached, and (3) the region of ionization by collision. In making ionization measurements care should always be taken to work only with saturation currents. An increase or decrease in voltage should not change the current. By applying this test a possible source of error can be avoided. The method of measurement described above makes it possible to measure the intensity of the Roentgen rays in absolute units, that is in electrostatic “e” units. In order to make the unit consistent Duane has proposed the following conditions: (1) The absorption of the Roentgen rays is to take place in one cubic centimeter of air at standard condi- tions : 0° C and 760 millimeter pressure. (2) The measurement must include not only the electrical effect of the primary ions produced in this cubic centimeter, but also the electrical effect of the secondary ions which are produced in the surrounding region. The second condition is necessary because of the fact that high velocity ions, chiefly electrons, are produced in the volume subjected to radiation and these ionize the sur- rounding air. Surfaces, metallic surfaces especially, 70 PRINCIPLES OF X RAY AND RADIUM DOSAGE must be so far removed that they are not reached by primary ions, that is to say, they must lie outside of the range of the primary ions. Otherwise ions strike the sur- face before they have transformed their entire energy into secondary ions. If this takes place, the measured intensity is too low. These conditions are best satisfied by the following apparatus: see Figure 13. QMJL*lJsvCta+\ - /. AU. Spectra, 161 K V, Constant Potential, Filtered (a) x/2 M M Cu, (b) 12 MM Al. (Duane.) The composition of the continuous spectrum depends on the direction in which the rays emanate. Wagner investigated this phenomenon and obtained the most reliable results. He examined the radiation emerging at the angles of 90° and 150°, as shown in Figure 22. At angles of 90° or less, maximum intensity and hard- ness was observed. At an angle of 150° or for radiation traveling in a backward direction, the intensity of the 104 PRINCIPLES OF X RAY AND RADIUM DOSAGE harder components is diminished by 37%, while that of the softer components is diminished by only 23%. Hence in this direction the radiation is not only less 3>A£.Z3L. Effect of Direction. intense but softer as well. The lower limiting wave length is the same for all directions, in agreement with the Planck-Einstein law. This fact becomes noticeable when measurements and irradiations are carried out at improper angles. A spectrum is determined to a large extent by the position of its two limits and its maximum, but not com- pletely, chiefly on account of the fact that a discontinuous spectrum is superposed on the continuous spectrum. The discontinuous spectrum consists of a large series of narrow lines, which occur in groups. For this reason the discontinuous spectrum is also called the line spec- trum. It has also been termed the characteristic spec- trum since it depends on the kind of material emitting the rays. The line spectrum exhibited by a tube with a tungsten target is different from that of a tube with a platinum target. The characteristic spectrum of an ele- ment is determined b its place in the periodic system of the elements. Each element can be given an “atomic DEFINITION AND MEASUREMENT OF QUALITY 105 number” depending on its place in the periodic system. The table given in Figure 23 gives the names, atomic weights and atomic numbers of all the known elements. Periodic System of the Elements. 73. Moseley found a simple relation between the wave length of the characteristic radiation and the atomic number of the elements. This relation is exhibited graphically in Figure 24. It is seen that the wave length decreases progressively with increasing atomic number. This relation is so exact that it can be used to determine where elements are still missing in the periodic system; for a missing element means a discontinuity in the curve. The relation found by Moseley can also be used to decide the correct order of those elements which on the basis of atomic weights would be placed in the reverse order. These elements are Argon—Potassium Cobalt—Nickel -f. Tellurium—Iodii j* Thorium—Protoactinum. 106 PRINCIPLES OF X RAY AND RADIUM DOSAGE The characteristic spectra are divided into the K, L and M series; of these the K series is the hardest; the L series is relatively soft and falls in the short wave length ——I -J 1 I Atomic Jiwmber iii, K Series L Series .ff Series Wave Lengths Spectrum of Uranium, i i i i i Fig: 24 AV. Relation between Characteristic Radiation and Atomic Number of the Elements. regions only for high atomic weights. The M series is extremely soft even for very high atomic weights and need not be considered in deep therapy. DEFINITION AND MEASUREMENT OF QUALITY 107 The K series consists of two lines, each of which is again complex. This is shown by the graphical represen- tation of the tungsten spectrum according to Duane (Figure 21). The wave lengths of the tungsten lines are important since they are convenient values for orientation in the spectrum, they are: aa 0.2135 A U ax 0.2088 A U Pi 0.1844 A U p2 0.1794 A U The figure also shows that the characteristic rays under the conditions used for deep therapy lie on the side of the maximum toward longer wave lengths, that is to say they make the total radiation softer. The character- istic K radition of uranium is much harder, it would lie on the shorter wave length side of the maximum and so increase the intensity of the hard radiation. This is one reason for the attempt to use uranium in place of tung- sten for the anticathode. Filters and protective substances also emit character- istic radiation when Roentgen rays strike them. The K radiation of copper, for instance, lies in the neighborhood of 1.5 A U which is in the region of the soft rays used for diagnostic purposes. Since they would be strongly absorbed by the skin it is advisable to absorb them with y2 or 1 millimeter of aluminum. The characteristic radia- tion of aluminum lies in the neighborhood of 8 A U. It is so soft that it does not reach the living layers of the skin at all but is completely absorbed by the overlying dead tissues and by the air. Doubtless characteristic radiation is also excited in the interior of the human body by the effect of the Roentgen rays on the hydrogen, carbon, oxygen and nitrogen atoms. The wave length of the 108 PRINCIPLES OF X RAY AND RADIUM DOSAGE characteristic K radiation of carbon and oxygen has recently been determined by Holtzmark and Kurth as 42.6 (42.9) and 23.8 A U. The wave length of the corre- sponding L radiation is 375 and 248 A U. Such rays are completely non-penetrating; they are at once absorbed and transformed into electronic motion. Lead also gives off characteristic radiation. Its K radiation is very hard, A, = 0.15 A U, hence penetrating and not dangerous. However, the L radiation of lead lies at 1 A U, between 0.79 and 1.35 A U. This soft radia- tion can in some cases do considerable damage. With sufficient filter thickness all primary radiation is absorbed; hence no characteristic radiation can be pro- duced on the side away from the tube. On the other hand a soft radiation comes from the side toward the tube; also when the filter is not of sufficient thickness characteristic radiation can emerge from the side oppo- site the tube. This soft radiation can be absorbed by rub- ber, leather or linen. For this reason lead should not be placed directly on the skin. The latter should be pro- tected with a cloth or rubber covering. This is also more sanitary and besides protects the patient against static charges. Also if radium rays are filtered through lead an intense secondary radiation is produced; it can be absorbed sufficiently by 0.2 millimeters of aluminum. Characteristic radiation of a given hardness is pro- duced only by the absorption of harder rays. The char- acteristic radiation of copper is excited only when rays of shorter wave length than 1.5 A U penetrate the copper. Again the characteristic K radiation of tungsten is excited only when a greater voltage than that corre- sponding to the K radiation of tungsten is applied to the DEFINITION AND MEASUREMENT OF QUALITY 109 tube. This phenomenon is very similar to the phenom- enon of fluorescence observed with ordinary light. The characteristic radiation is therefore also called fluorescent radiation. In the following table the average wave lengths of the characteristic radiations of a number of important elements are given: Ele- ment K(S Ka Ele- ment KP Ka A1 7.96 A U 8.30 A U Wo 0.180 A U 0.210 A U Cu 1.39 A U 1.54 A U Ir 0.168 A U 0.188 A U Zn 1.30 A U 1.44 A U Pt 0.159 A U 0.183 A U Ag 0.50 A U 0.56 A U Ur 0.108 A U 0.130 A U Sn 0.43 A U 0.49 A U Pb 0.14 A U 0.16 A U Pb L 1.0 A IJ The elements in the left hand column are of importance as filters and protective material: those in the right as anticathode metals. On account of the complex mixture of discontinuous and continuous spectra in an ordinary spectrum it is impossible to estimate or deduce an average value of the wave length from which conclusions as to the general properties of the radiation could be drawn. However, for the purposes of deep therapy a knowledge of the average hardness is more important than a knowledge of the composition of the beam. Acting on this idea Duane has introduced the con- cept of effective wave length. In any unhomogeneous beam there always exists a homogeneous radiation of a definite wave length, which would be absorbed in the no PRINCIPLES OF X RAY AND RADIUM DOSAGE same ratio by a given filter, say 4 millimeters of alum- inum, as the beam as a whole. A really heterogeneous radiation can therefore be thought of as replaced by a homogeneous radiation of a definite wave length. lAnd-strorn- t/ntfs Wave lend tlx Ae in Fig 25 Percentage of Roentgen Rays Passing Through 1 MM Copper and 4 MM Aluminum for Various Effective Wavelengths. DEFINITION AND MEASUREMENT OF QUALITY 111 Duane defines the effective wave length of a mixed beam as the wave length which shows the same property (absorption in aluminum or copper of a definite thick- ness) as the mixture. He proposes that the percentage of radiation penetrating 4 millimeters aluminum or 1 millimeter of copper be determined. From the curves given in Figure 25 together with an absorption meas- urement the effective wave length can be deduced. The absorption measurement is best carried out with an elec- troscope as follows: The regular filter, say millimeter copper and 1 millimeter of aluminum, is put in place; one measure- ment is made without the auxiliary filter (4 millimeters aluminum) and a second made with the auxiliary filter. The measurements are made alternately a number of times about as follows: No filter mm A1 13.6 16.6 13.5 Discharge time 13.8 16.9 16.8 13.5 Average value 13.6 16.8 Ratio 81. 100 The two discharge times 13.6 and 16.8 are in the ratio of 81 : 100. Now the intensities are in the inverse ratio—a long discharge time corresponds to a low intensity. The intensities are therefore in the ratio of 100: 81, i.e. 81% of the incident radiation is transmitted by the filter, the 112 PRINCIPLES OF X RAY AND RADIUM DOSAGE remainder, 19% being absorbed. Next, the value corre- sponding to a penetration of 81% is read off from the graph. One follows the vertical line at 81 upward to the curve and then proceeds along the horizontal line to .15 A U. If the same measurement is carried out with a copper filter, it is found that 55% of the incident radiation is transmitted, which from the curve at the left gives a value of 0.14 A U. The difference in wave length is explained by the greater absorption of soft rays by the heavier filter. Human tissue also filters out the soft com- ponents. As far as the hardness of the radiation is con- cerned, a filter of 4 millimeters of aluminum corresponds to a thickness of tissue of 3 to 3.5 centimeters, a filter of 1 millimeter of copper to 7 to 7.5 centimeters of tissue. Hence the aluminum filter is a better measure of the effective wave length near the surface; the copper filter gives us more information about the effective wave length at a greater depth. A statement of the effective wave length is a very sim- ple and practical definition of the hardness of the radia- tion; it is based on an absorption measurement and therefore can be used to give information regarding the depth distribution, which also depends on absorption. The measurement of the effective wave length by absorp- tion is much simpler than any other method for the meas- urement of hardness. §2. Practical Definitions of Hardness. In Roentgen ray practice the endeavor to attain a simple method of describing the penetrating property of the rays has led to a number of definitions of hardness or penetration. DEFINITION AND MEASUREMENT OF QUALITY 113 The attempt here has not been to formulate a theoret- ically exact definition of quality but rather to obtain a working definition of the penetration of the rays into the tissues, taking into account the various factors which influence this penetration. These factors are: (a) Focus skin distance; (b) Absorption; (c) Scattering. That the focus skin distance is an important factor in determining the penetration of the rays into the tissues is easily seen from the following example: (a) In place of the patient a phantom consisting of an air filled sphere 20 centimeters in diameter is used; the distance between the target and the surface of the sphere is made 30 centimeters; and the intensity at the surface is taken as 100. What will be the intensity at the center, that is at a depth of 10 centimeters? According to the inverse square law x: 100 = 302: (30+ 10)2 = 302 : 402 = 9: 16 ==0.56 x = 56%. Now let the distance be increased to 50 centimeters, but let the intensity at the surface be made the same as before by increasing the milliamperage. What will now be the intensity at the center? x: 100 = 502: 602 = 25:36 = 0.695 j; x = 69^%. 114 PRINCIPLES OF X RAY AND RADIUM DOSAGE The intensity at the same depth relative to the inten- sity at the surface is therefore appreciably greater with a greater focus skin distance. This result can be verified with an iontoquantimeter. (b) Next let us make the following experiment (Fig- ure 26): '2/ic&t£A^ Zb, The Effect of Scattered Radiation on the Depth Dose. The measuring instrument is placed SO centimeters from the target and a box some 10 centimeters high, which can be filled with water, is interposed. Two lead diaphragms, each with a circular aperture 1 centimeter in diameter, are placed one above and one below the box. Measurements are made both with the box empty and with the box filled with water. They show that DEFINITION AND MEASUREMENT OF QUALITY 115 approximately }i (accurately 19%) penetrates the water, the remainder or 81% is absorbed by the water. It is important to note that the distance of the chamber from the target was not changed during the experiment. Hence it is immaterial whether a distance of 50 centi- meters or one of 30 centimeters is used. In this case the total loss of intensity is the result of absorption of the rays in the water. The amount of absorption depends on the wave length of the radiation; the exact relation between the two is given in Chapter III. (c) Now let both diaphragms be removed and let the measurements be repeated with and without water. Instead of a narrow pencil of rays a broad beam now passes through the water. The intensities with and with- out the water are now found to be in the ratio of 100 : 45, i. e., 45%, now passes through and 55% is absorbed. The difference in results obtained in experiments (b) and (c) is explained by the fact that there are two kinds of absorption; true absorption and absorption due to scattering. (1) True absorption is a transformation of the energy of Roentgen radiation into other forms, such as soft char- acteristic radiation, ionic and electronic motion, heat, etc. The soft characteristic radiation of water is immedi- ately absorbed at the point where it originates and is transformed into electronic motion. The electronic motion also goes over into heat; in some substances chemical changes occur; in living tissues biologic reac- tions are produced; and all these phenomena involve a loss of primary Roentgen energy. This loss due to trans- formation is called true absorption. (2) Absorption due to scattering: Roentgen rays are bent from their course whenever they pass through 116 PRINCIPLES OF X RAY AND RADIUM DOSAGE matter; that is, they are scattered. If a narrow pencil of rays passes through matter, these scattered rays are lost to the pencil, they merely give up a small amount of energy to the surrounding medium. If, however, a large volume is subjected to radiation the scattered rays pro- ceeding from any one pencil add to the primary radiation adjacent. What is lost by one pencil of the beam is com- pensated for by the neighboring pencils; this is especially true for the central ray around which the primary radia- tion is uniformly distributed. On this account a much smaller loss of absorbed energy is found by a measure- ment. In experiment (b) the absorption found for the nar- row beam is due to both true and scattered absorption. In example (c) most of the scattered energy is returned and we have practically only true absorption. Experiment (c) can be still further developed, see again Figure 26. A second water phantom is placed behind the ionization chamber, where before there was no scattering medium. A new measurement shows that the intensity has increased from 45% to 56%. By the medium which now completely surrounds the chamber an additional 11% is reflected back to it. The chamber now lies entirely within a scattering medium and receives the maximum of scattered radiation. These examples show on what factors the intensity in the interior of a medium depends. In these particular instances water was used as the absorbing medium. Experiment and theory have shown that body tissue behaves on the average toward Roentgen rays and radium rays much the same as does water. In Chapter III the behavior of other matter toward Roentgen rays will be further discussed. DEFINITION AND MEASUREMENT OF QUALITY 117 Absorption and scattering have a definite relation to the wave length and can therefore serve as a measure of the quality of the radiation. However, other factors, like the focus skin distance and the volume subjected to radia- tion, somewhat complicate the relations. With this idea in mind we shall discuss a few of the hardness definitions used in practice. (a) The “percentage decrease per centimeter” gives the decrease of intensity in per cent from centimeter to centimeter. This decrease depends (1) On the wave length of the radiation. Not only the average (effective) wave length but the composition of the beam is a determining factor. (2) On the focus skin distance—the larger the focus skin distance the smaller the per cent decrease. (3) On size of field—large fields show a smaller decrease. (4) On the depth—the decrease is not uniform; it is smaller in the first centimeter than in the deeper ones. The exact relations are shown in Chapter III. (b) The “half value layer.” This is defined as the depth (in centimeter) at which the intensity is reduced to half its value at the surface. This depends on (1) Effective wave length (2) Focus skin distance (3) Size of field. (c) The “depth dose.” This is defined as the intensity at 10 centimeters depth expressed in per cent of the intensity at the surface. A depth dose of 40% means that 40% of the intensity at the surface reaches a depth of 10 centimeters. 118 PRINCIPLES OF X RAY AND RADIUM DOSAGE The depth dose depends on (1) Effective wave length (2) Focus skin distance (3) Size of field. In all cases cited the extent of the surrounding medium (diameter of patient) also enters as an important factor. The depth dose is the most widely used definition of penetration; for this reason the experimental determina- tion of this quantity will be discussed in detail. The best apparatus for this purpose is an ionto- quantimeter with a small chamber. In order to make the measurement accurate, the chamber must be of small dimensions and must be symmetrically surrounded by water or a similar substance. Metallic substances, which absorb strongly and scatter considerably, should not be placed in the immediate neighborhood of the chamber. An iontoquantimeter constructed by the author satis- fies these requirements. (Figure 15.) Iontoquantimeters with large boxlike chambers do not measure the complete scattered radiation and give results about 15% low for the depth dose. The selenium cell of Fuerstenau also does not measure the full amount of scattered radiation and gives too low a value for the depth dose. Electroscopes of course cannot be used for these measurements. The iontoquantimeter is best used with a water phan- tom. Wooden cubes filled with water are very conven- ient. Bodies of various shapes can be built up out of them and measurements made at various depths and along at the sides. With a water filled container only rays coming from above can be measured conveniently. DEFINITION AND MEASUREMENT OF QUALITY 119 In setting up the apparatus a number of sources of error must be carefully avoided. (1) For surface measurements the chamber must not lie above or below the surface. In the first position too little and in the second too great an intensity would be measured. The third position gives approximately cor- rect values. For this reason a wooden (oak) board cut to receive the chamber and of about half the thickness of the chamber is used. The surface of this board and there- fore the center of the chamber must be at the chosen focus skin distance from the target (50 centimeters). SO cm. 60 cm. 10 cm. ns*7- Correct Measurement of the Depth Dose with a Small Ionisation Chamber. 120 PRINCIPLES OF X RAY AND RADIUM DOSAGE (2) In passing from the surface to the depth meas- urement, the chamber must be lowered exactly 10 centi- meters. (3) Also at a depth the chamber must be surrounded by the scattering medium. Above the chamber there must be exactly 10 centimeters of the medium, below the chamber at least this distance, and toward the sides a greater distance than 10 centimeters. The exact arrangement is shown in Figure 27. It is seen that with this arrangement the increment in focus skin distance as well as the increment in the irradiated medium is exactly 10 centimeters. If a chamber 2 centimeters in thickness were immersed 10 centimeters below the surface, only 9 centi- meters of absorbing substance would be interposed; if 10 centimeters were interposed, the increment in focus skin distance would be 11 centimeters. These sources of error are avoided by the above arrangement. At the surface, as well as at a depth of 10 centimeters, the measured discharge time must be corrected for leak discharge according to the formula given in Chapter I. If the corrected value of the time at the surface is t» and that at a depth ta then the intensities are in the inverse ratio and the depth dose in per cent is given by: D = 100 — td Similar measurements can be made of the hardness or of the depth distribution of radium rays. The rapid change of intensity, due to the smaller distances used in radium technique, makes it necessary to employ very small chambers. On account of the resulting small ion- ization current, the measuring instrument must be very sensitive and well shielded against the penetrating gamma rays. DEFINITION AND MEASUREMENT OF QUALITY 121 As the last of the practical definitions of quality let us consider the total absorption coefficient p. While the various definitions considered so far are not accurately defined but depend on a number of factors, the total absorption coefficient is independent of the focus skin distance and size of field. Let us refer again to the above experiment on the absorption of a narrow pencil of rays by water. If the water phantom is interposed without changing the dis- tance between target and chamber the result of the meas- urement is entirely independent of this distance. On account of the small cross section of the beam no appreci- able amount of scattered radiation returns from the inte- rior of the water. Hence this measurement gives the total absorption resulting from the addition of true absorption and absorption due to scattering. The defini- tion of the absorption coefficient is given by a formula, the derivation of which cannot be discussed here, but which can be used for the measurement and the computa- tion of p. The formula is log — tf 14 “ d X 0.4343 where to is the discharge time without the absorbing medium and tf with the absorbing medium, d is the thick- ness of the absorbing layer in centimeters. The calculation is simplest if a layer 2.3 centimeters thick is used, for then the denominator becomes equal to 1 and the formula becomes i H = log — tf 122 PRINCIPLES OF X RAY AND RADIUM DOSAGE The best method for determining p is that employing the electroscope. For this purpose an electroscope with a long entrance tube provided with two diaphragms is used and a water phantom 2.3 centimeters in thickness is inserted between the two diaphragms. The arrangement is shown in Figure 28. jfJUaA. il f 1±= Gj ifaajJL 2u 1/ i. o 7.y i.o ~7'fr/<)LAs4-J2a^- AIL. Absorption Curves of Copper and Silver. DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 131 The full curve shows the variation of the absorption with the wave length for copper. It will be noticed that the curve is discontinuous at one point; with increasing wave length the absorption suddenly decreases to very low values. In this region softer rays are actually absorbed to a lesser degree than the harder ones. Every element has a characteristic discontinuity in its absorption curve. This point lies just below the point of characteristic emission. The following table gives the characteristic K wave lengths and the edges of the absorption bands, as these points of discontinuity have come to be known, for a few elements useful in Roent- gen practice. Element Atomic Number X Absorption Band Xa xp A1 13 7.9470 A U 8.30 AU 7.96 AU Cu 29 1.3785 A U 1.54 AU 1.39 AU Zn 30 1.2963 A U 1.44 AU 1.30 AU Pb 82 0.1412 A U 1.16 AU 0.14 AU Wo 74 0.1783 A U 0.210 A U 0.180 A U Ir 77 0.167 AU 0.188 A U 0.168 A U Pt 78 0.1582 A U 0.183 A U 0.159 A U Ur 92 0.1075 A U 0.130 A U 0.108 A U Br 35 0.9179 A U 1.035 A U 0.929 A U Ag 47 0.4850 A U 0.562 A U 0.501 A U The table shows that the region of transparency and characteristic radiation for copper lies above 1.37 A U, for zinc lies above 1.29 A U. An aluminum filter readily absorbs these wave lengths. Its characteristic radiation and region of trans- parency is in the range of extremely soft rays: namely, above 8 A U. 132 PRINCIPLES OF X RAY AND RADIUM DOSAGE The table shows also that lead cannot be considered for filter material; its point of discontinuity lies inside the range of wave lengths used for deep therapy. That is to say, in this range lead absorbs hard rays and trans- mits soft rays. Also all the elements used for anti- cathodes: tungsten, iridium, platinum, uranium, are not to be recommended as filters. Besides copper, silver is used for filtering radium rays. The two absorption curves of these metals dove- tail well, as a glance at Figure 29 will show. How- ever, the silver should not be used alone as it emits and transmits medium soft rays. Silver and bromide play an important part in spec- trum photography and in photographic measurements of intensity and energy: On every spectrum photograph two points of discon- tinuity are observed, corresponding to the wave lengths 0.485 A U and 0.918 A U. One of these is illustrated in Figure 20. At a point corresponding to the wave length 0.485 A U, the blackening changes abruptly from a dark to a light shade. This phenomenon is due to the selective absorption of the silver in the photographic emulsion. Silver absorbs those rays whose wave lengths are less than 0.485 A U more strongly than it does those whose wave lengths are greater than 0.485 A U. This defect of the plate is not likely to become a source of error in spec- troscopy since the phenomenon is now well known. These places of discontinuity can, moreover, serve as convenient reference points. However, the situation is very different from photographic films (Kienboeck strips) are used for measuring intensity. If the intensities of two radiations, one of which has DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 133 a wave length lying above the point of selective absorp- tion and the other of which has a wave length lying below it, are compared by the photographic method, the harder radiation will be measured too strong relative to the other. The photographic measurement in this case is subject to an error due to the effect of hardness. All measuring instruments are subject to errors due to hardness—the Fuerstenau intensimeter, for example, due to the use of selenium as the active material. The point of discontinuity in the selenium absorption curve is at 0.99 A U. The conducting wires, as well as the core on which they are wound, and the carton, which encloses the whole, cause errors due to selective absorption. On account of this fact correction factors must be used for different wave lengths. These will be discussed in Chap- ter IV on relative dosage. For practical dosage it is of importance to use an instrument which is not subject to errors due to varying hardness, or, still better, one which has the same hardness factor as the biologic object —the tissues or the skin. The biologic object absorbs hard and soft rays very differently; if there is an instru- ment which reacts in the same way to various hardnesses, then a close relation ought to exist between the readings of this instrument and the biologic reaction. Now there are substances which can be used for this purpose. First of these is, of course, the biologic specimen itself. The great significance of the experiments of Juengling on beans, those of Wood on mouse tumors, and those of Kroenig and Friedrich on frog larvae, lie in the avoid- ance of the error due to hardness. Hence these methods are to be recommended for comparing the biologic effect of rays of different hardness. These methods have the advantage that systematic errors are absolutely excluded; 134 PRINCIPLES OF X RAY AND RADIUM DOSAGE however, the disadvantage that they lack the accuracy and convenience of the physical methods. Another substance which can be used for measure- ments and which does not show any serious errors due to hardness, is air. Air consists of elements of atomic numbers 7 (nitrogen), 8 (oxygen), 1 (hydrogen), etc. Hence it has almost the same average atomic number as body tissue, whose average atomic number lies between 7 and 8. For this reason air and tissue show about the same hardness factor; the absorption of hard and soft rays takes place in about the same ratio in the two sub- stances. This behavior of air is important since air serves as the active agent in ionization chambers. As far as the absorption of Roentgen rays is concerned, the effect in air is proportional to that in tissue. However, there are a number of factors which may lead to errors. First of all, the total amount of absorbed energy is not converted into ions but only a fractional part, which varies with the wave length and which is not definitely known. Further, the ions produced have different ranges. While in the tissues, with both hard and soft rays, dissociation takes place only at the point where the energy is absorbed, in air the secondary ions produce additional ions at various distances, depending on the wave length. Again, the Roentgen rays on entering and leaving the chamber excite characteristic radiation on the walls of the chamber. All these factors combined cause the ratio of ionizing to biologic effect to vary with the hardness. However, Holthusen has succeeded in controlling this hardness factor by calculation and Fried- rich has constructed a small chamber of horn which has been experimentally so adjusted that it practically obvi- ates the error due to hardness, at least over a definite DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 135 range of wave lengths. The readings obtained with such a chamber are valid, therefore, for various degrees of hardness. The absorption also depends on the physical prop- erties of the absorbing substance. The density and atomic number are determining factors. The value of the absorption coefficient is directly proportional to the density and inversely proportional to the third power of the atomic number. For this reason the true absorption increases very rapidly with the atomic number. The table below gives the atomic number, the density, the true absorption coefficient, and the ratio of absorp- tion at the wave length 0.2 A U for a few elements of interest. These values are calculated according to the formulas: a — 0.0195 N 2,58 d • X 2 8 for wave lengths below this point of discontinuity of the absorption curve; and a = 0.0004 N 314 d • X 2,8 for wave lengths above this point. The second formula need only be used in the case of lead. Element Atomic number i OT 0.074 A U 0.19 A U Water Ishino 0.04 AU 0.12 A U Al Water, Al, Neukirchen 0.04 AU Y Glycerin, Tur- pentine DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 137 For water = a, since the density of water is equal to unity. Compared to jl, a changes little with the wave length. Hence for soft rays o becomes negligible in comparison with a and the total absorption is practically determined by jl alone. This is particularly true of the heavy ele- ments, filter and diaphragm materials, since the true absorption increases with both the atomic weight and the density while the scattering is proportional only to the density. For these metals the scattering can, in gen- eral, be neglected. The reverse is true for very hard rays. The true absorption can here become less than the scattering so that the latter becomes the primary factor in determin- ing the total absorption. This is particularly true of the substances composed of elements of low atomic number, for example: water, air, and tissue. These substances scatter more than they absorb. Their behavior is deter- mined almost wholly by a. Since the total absorption depends on the sum of jl and g, the preliminary values given in the table on page 135 must be replaced by more correct ones: The ratio of true absorption of water and of alum- inum was found to be about 1 : 8. The coefficients of scattering are in the same ratio as the densities namely, 1 : 2.7. Since in the case of soft rays the true absorption is the determining factor, we find that the two substances absorb soft rays in the ratio 1 : 8. On the other hand with very hard rays, the y rays of radium, for example, the ratio is determined by the scat- tering alone and is approximately as 1 :2.7. 138 PRINCIPLES OF X RAY AND RADIUM DOSAGE For intermediate wave lengths the ratio of absorption of the two substances varies continuously from the one extreme to the other. The following table give the exact values: Hardness Aluminum H Water Ratio Soft 5.6 0.7 8 Middle hard 1.08 0.21 5.1 Hard 0.S2 0.17 3.0 Y rays 0.115 0.043 2.7 Hence we cannot speak of a univalent ratio between the absorption of water and that of aluminum. This ratio varies and must be determined for every mixture of rays. The situation is the same with aluminum and copper. With 200 K V, 0.5 millimeters of copper corresponds to 12 milli- meters of aluminum; 1.0 millimeters of copper corresponds to 22 milli- meters of aluminum. For 130 K V the following table applies: Cu filter A1 filter Ratio 0.1 mm 3.0 mm 30 0.2 mm 5.5 mm 28 0.3 mm 7.8 mm 26 0.4 mm 10.0 mm 25 0.5 mm 12.0 mm 24 Copper filters the soft rays about 29 or 30 times as strongly as aluminum; while it absorbs the hard rays only about 22 times as strongly. With copper, there- fore, a better filter action is attained. This has already DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 139 been mentioned in the discussion of the intensity curves of Duane (see Figure 21). The explanation of the general trend of these curves will now be evident. The values given for other substances are also modi- fied by the scattering. The table below gives the total absorption coefficient and the half value layer for a radiation which is obtained with 200 K V, 1 millimeter of copper plus 1 millimeter of aluminum. The ratio of the absorption of various metals is also given: Material Half value layer Ratios Water .17 4.1 cm 1 A1 .52 1.3 cm 3 1 Cu 6.0 0.12 cm 12 1 Zn 5.5 0.13 cm 11 0.9 Pb 30. 0.023 cm 5 Connective tissue .168 4.1 cm 1.00 Fat tissue .152 4.6 cm 0.90 Bones .181 3.9 cm 1.08 In this case the ratio of aluminum to copper absorp- tion is found to be 1: 12 compared to 1:22 as given before. The reason for this is that with the radiation used above the soft rays have already been filtered out by the regular filters (1 millimeter copper plus 1 milli- meter aluminum) before the mixture is examined; while in the preceding instance the unfiltered radiation was examined directly. The table shows, in addition, the close agreement between the absorption of water and that of the tissues. This should be the case also theoretically since not only is the density of the two substances the same but also 140 PRINCIPLES OF X RAY A'ND RADIUM DOSAGE the average atomic weight, inasmuch as the tissues are composed of elements of low atomic numbers, namely, between 7 and 8. The deviations observed with bony and fat tissue are in opposite directions and will in general offset each other. Air spaces can decrease the total absorption by about 15%. Experimental comparisons of the absorption of vari- ous tissues have been made by Nick and Schlager. The following table gives the values reported by these authors for hard rays; the absorption of water is arbi- trarily set equal to 100. Tissue Absorption Density Water 100 1.00 Fat tissue 53 ? .97 Blood serum 103 1.03 Brain 107 1.04 Muscles 100 1.05 Lungs 86 1.05 ? Heart muscle 106 1.05 Kidney 106 1.05 Liver 107 1.06 Spleen 112 1.06 The table shows that only slight deviations from the mean and from the value obtained with water occur. The low value for fat tissue is probabfy incorrect; it is contradicted by measurements made by the author and would not be expected from the density and composition of fat tissue. The density of the tissues of the lungs appears to the author to be too high. The next table compares a series of substances with regard to absorption. The figures give the percentage of radiation passing through layers of various thick- DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 141 nesses, provided the distance between the ionization chamber and the Roentgen ray tube is not changed. The measurements were made with 200 K V, 1 millimeter of copper plus 1 millimeter of aluminum and were carried out with an iontoquantimeter. Material 1 cm 2 cm 5 cm 10 cm 15 cm 20 cm % % % % % % Water 92 85 68 45 30 20 Oak 94 88 74 55 Ebony 90 82 61 37 Balsa 98 96 92 84 Brickstone 74-76 56-58 24-25 6-8 1.3 0.3 Concrete 72-75 50-54 17-23 3-5 0.5 0.2 Nearly all woods absorb less than water, but only slightly less. The absorption corresponds fairly well to the density. Ebony is the only one heavier than water; for this reason it also absorbs more than water. By gluing together equal thicknesses of ebonite and oak a very good wood phantom of bodily tissue can be pro- duced. Wood is often used for mechanical support when the patient is treated from below on a mattress. Most woods are unsuitable for this purpose since they absorb too heavily (10-12%); balsa wood is a good material for this purpose as its absorption is hardly appreciable. A thickness of 2-3 centimeters must be used. An aluminum filter is, of course, superfluous in this case since the wood absorbs the secondary rays of the copper. Balsa wood is also used as a holder for radium preparations. It can easily be carved into any form and used to maintain a definite distance between the radium and the skin with- out absorbing the hard y rays appreciably. The values given for brick and concrete show that very thick walls 142 PRINCIPLES OF X RAY AND RADIUM DOSAGE are necessary to absorb all the radiation. About 1% of the incident radiation passes through a 15 centimeter (6 inch) wall. For the protection of the operator an absorption of 99% is not sufficient; the transmitted radiation should be reduced to 1/1000 or less. Hence lead covering is necessary. The author has made a series of measurements on the ordinary protective materials with various trans- formers, voltages and filiations. For 190-210 K V and 3/4-4/4 millimeter of copper the values given in the following table apply; these values give the intensity in percent of the intensity which would exist if the protective material were not present. Material 1 mm 2 mm 3 mm 5 mm 10 mm 20 mm Lead 7-10% Lrl% l-2°/00 l0/ 1 / 00 Lead glass 30-35% 15-20% 2-4% 1-2% Lead rubber 40-50% 20-25% 7-10% 3-5% WWo With the help of this table one can determine the amount of protective material required. Special precau- tions should be taken with rooms in which there are employes. Only 1/1000 or less of the incident radia- tion must be allowed to pass through the walls. For this reason walls of considerable thickness should be covered with \y2 or 2 millimeters of lead; wooden walls should be covered with 3-4 millimeters. A thickness greater than 5 millimeters of lead is unnecessary with the radia- tions used at present. The lead glass used for the small window which gives the operator a view of the treat- meant room need not be as heavy since the aperture allows only a small beam to pass through. A thickness of 10 millimeters is sufficient; more than 15 millimeters is overdoing protection; with large windows, which DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 143 might expose part of the operator’s body to the radia- tion, a thickness of 20 millimeters should be used in order not to allow a penetration of more than 1/1000. For the protection of the patient during the relatively short exposure time a protective material which allows less than 3% to pass through is sufficient. For this purpose a thickness of some 2 millimeters sheet lead or 5 milli- meters of leaded rubber is ample. Metallic lead should not be placed directly on the skin on account of the sec- ondary radiation. With even an insufficient thickness of protective material there is little danger of harming the skin; however, a relatively large energy would be sup- plied to the total volume of the body and this would unnecessarily aggravate the ray sickness. The values given above will enable an approximate solution of any problem involving protection; more exact calculations are hardly possible on account of the many complications which occur in any specific case. A few general remarks may not be out of place. According to Halberstadter every Coolidge tube sends out in the reverse direction a radiation which is softer than that proceeding in the forward direction (that of the central ray) and the intensity of which is about 1/7 that in the forward direction. Every object struck by radiation scatters rays of prac- tically the same hardness as the incident radiation and further emits softer (characteristic) radiation. If not protected against this stray radiation, the total surface of the patient receives an amount of energy equal approximately to 1/30 of that applied at the port of entry. If an erythema dose is denoted by 100%, the total surface of the patient receives 3%. The patient should be protected against this stray radiation not because of 144 PRINCIPLES OF X RAY AND RADIUM DOSAGE its effect on the skin, but because of the effect on the gen- eral reaction of the patient. The patient being treated also scatters radiation; the order of magnitude of the latter with a large port of entry, is approximately 1/10 of the energy supplied to the region directly rayed. At a distance of 50 centimeters to one side of the patient the intensity amounts to 1%. Hence the patient can, as a first approximation, be regarded as a source of radiation, the intensity of which is about 1/100 of that emitted by the Roentgen ray tube with filters. Against this radiation the operator must, of course, be protected. In the consideration of protection against radium radiation a distinction must be made between the easily absorbed a, p, and soft y rays, and the hard y rays. Pro- tection against the first group can be attained with strong absorbing materials: lead, barium-concrete, etc.; protec- tion against the hard y radiation is given only by distance. The customary protective measures, namely, the handling of radium preparations with tweezers and the carrying of radium preparations in lead containers, are well known. §2. Laws of Distribution. We now come to the discussion of the distribution of the radiation. Since the distribution depends on a number of factors, it is necessary to discuss these factors separately before taking up the actual distribution in a number of examples. The distribution of the radiation is dependent on (1) The law of inverse squares. (2) The law of absorption. (3) The scattering. DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 145 In the following we shall endeavor to synthesize the actual distribution from its components. (1) The law of inverse squares enables us to calculate the distribution along the central ray if we temporarily ignore the absorption and the scattering. In Chapter II it has already been shown, that with increasing focus skin distance, the distribution at a depth becomes more favor- able. Of course, in order to obtain the same surface energy the time of radiation must be increased by an amount which is easily calculated. Let us set the energy which the surface receives at all focal distances arbitrar- ily at 100; then the curves of Figure 30 give the intensities at various depths, on the basis of the inverse square law alone. The greater the distance, the greater the depth dose, and the better the distribution in the interior; however, with increasing distance the exposure time becomes more and more uneconomical. It has been found that in the treatment of malignancies 50 centi- meters is the most practical focus skin distance, at least with the present apparatus. Cm FSD. Intensity Fig: 30 cm depth Intensities at Various Depths for Various Focal Distances, Accor- ding to the Inverse Square Law, Absorption Neglected. 146 PRINCIPLES OF X RAY AND RADIUM DOSAGE If in the future the milliamperage should be increased to 30 milliamperes, the focus skin distance could be increased, since the time loss would no longer be of significance. An increase of the kilovoltage to 250 K V would increase both intensity and hardness. In this case also a small increase in focus skin distance would be appropriate. For some treatments which require less intensity in the interior a distance of 30 centimeters is appropriate. In changing from one focal distance to another the following table can be utilized: Focus skin distance Time Depth dose, per cent 30 cm 36 (Min) 24 28 32 36 40 40 cm 64 (Min) 28 32 37 41 46 50 cm 100 (Min) 30 35 40 45 50 60 cm 144 (Min) 32 37 42 48 53 70 cm 198 (Min) 33 39 44 50 55 The last table, moreover, takes into account both absorption and scattering; without these, greater depth doses would be expected. (2) The distribution resulting from total absorption when neither the law of inverse squares nor the scatter- ing is taken into account, i.e., when the distance is very- great and the port of entry very small, is given by the following law: In every centimeter the same percentage of the inci- dent radiation is absorbed (transformed and scattered). Figure 31 shows this very clearly for two different hardnesses. The figure shows a series of important facts: (a) The same percentage of the incident radiation is absorbed in each layer. DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 147 (b) The energy absorbed per centimeter, or better, per cubic centimeter, is therefore proportional to the transmitted intensity. A°p- /KmJL Fi(k.3t. Depth Distribution of Applied and Absorbed Energy for Soft and Hard Rays. (c) If two radiations of equal energy but of different hardness are applied, then the softer radiation is more strongly absorbed in the upper layers, and for this reason soft rays produce a greater biologic reaction near the surface. (d) For the same absorbed energy in the surface layer, the energy absorbed at various depths decreases more rapidly with soft rays than it does with hard rays. Since the reaction of the skin and of malignant tumors is determined primarily by the absorbed energy, it is readily seen why the hard rays are more effective in deep therapy. 148 PRINCIPLES OF X RAY AND RADIUM DOSAGE The foregoing considerations show that for rays of one and the same hardness it is immaterial whether the intensity or the absorbed energy is used for describing the depth distribution or predicting the biologic reaction. The same numerical result is obtained in either case. On the other hand, in comparing hard and soft radiations the absorbed energy must be used as the basis if a hard- ness error is to be avoided. The data given in the tables can be made more com- prehensive by means of curves. (Figure 32.) The ordinates represent the intensities, the abscissa the depth within the tissues. These curves are called exponential curves. They have the property that for equal distances along the abscissa the ordinates decrease by equal percentages. Such curves and all the preceding considerations apply only to homogeneous rays. In practice, however, a mix- ture of rays of different wave lengths, that is, a more or less unhomogeneous or heterogeneous beam is dealt with. On their way through the tissues heterogeneous beams lose their softer components more rapidly than they do their harder ones. The absorption at the begin- ning is therefore determined by all components, while at a depth it is determined primarily by the hard com- ponents. The absorption curve is no longer exponential; the absorption may at first be 18 per cent per centimeter while in the deeper layers it may be only 11 per cent. The curve of such a mixture is shown by the dotted line in Figure 32. The heterogeneity is most accurately defined by the spectral composition of the beam. In practice a more convenient definition is, however, the ratio of the first two half value layers. DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 149 For homogeneous rays the half value layer does not change as the rays penetrate into the tissues. This is shown by Figure 32. The intensity of the hard radia- tion changes from 100 per cent to 50 per cent at a Intensity TV 3 2 cm. depth Intensity Curves and Half Value Layers of Hard and Soft Homo- geneous Rays, and Mixed Unhomogeneous Rays. depth of 6.5 centimeters. It is reduced from 50 per cent to 25 per cent in the next 6.5 centimeters. Hence the first two half value layers are equal. The quotient of the two is equal to one. The same holds for the soft radiation. For the unhomogeneous radiation (dotted curve of Figure 32), however, the first half value layer is 3.9 centimeters and the second 6.7 centimeters. If we divide one by the other we get h2 67 1 7 ' 3.9 This quotient is called the factor of heterogeneity. It is a measure of the heterogeneity of the radiation. ISO PRINCIPLES OF X RAY AND RADIUM DOSAGE For homogeneous rays the factor is equal to 1. In some text books a so-called point of homogeneity is mentioned. It is defined as the point at which the radiation ceases to be heterogeneous and becomes homo- geneous. Such a point exists neither theoretically nor experimentally. In the above absorption curves the law of inverse squares, which has been discussed in the preceding chap- ter, was not taken into account. A combination of the two curves can be effected by multiplying together corre- sponding values, reducing the first product to 100 by dividing by the proper number, and reducing all the other products in the same ratio. As an example the 50 cm focus skin distance curve is combined with the curve representing the homogeneous hard radiation (p = 0.167; h = 4.2 cm) as follows: 0 centimeter 100 X 100 10000 reduced to 100 2 centimeters 73 X 93 6800 reduced to 68 5 centimeters 44 X 83 3650 reduced to 36 10 centimeters 19 X 69 1310 reduced to 13 20 centimeters 4X 51 204 reduced to 2 Intensity Calculated Intensity Curves. Fig' 33 cm. depth DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 151 Figure 33 shows the resulting values as an intensity curve for very small fields (pencils of rays); this calcu- lated curve agrees very closely with the results of actual measurements. (3) However, the larger the size of field the more does the scattered radiation increase the values in the interior of the rayed volume. From the interior a part of the scattered radiation penetrates the region not rayed directly and a part is also scattered back to the surface of entry. The theory of scattered radiation is not yet sufficiently developed to enable an exact calculation of the scattered component. Moreover, there are still uncertainties in the experimental determination of this quantity; so far it has been assumed that the scattered radiation has the same hardness as the primary radiation. Recent measurements by Compton show, however, that the scattered radiation contains softer components besides. Exact measurements have shown that the scattered radiation increases the intensity at the surface as fol- lows : (200 K V, 1 mm copper) With ( 0 centimeter )2 P of E, about 0% With ( 5 centimeters)2 P of E, about -\-l6% With (10 centimeters)2 P of E, about +30% With (15 centimeters)2 P of E, about +42% With (20 centimeters)2 P of E, about +50% With (25 centimeters)2 P of E, about +52% With small ports of entry the scattered component increases very rapidly with an increase in size of field. With large ports of entry it approaches a maximum, which corresponds to the greatest amount of energy scattered back. In the interior this increase of energy, due to the addition of scattered radiation, is still greater. 152 PRINCIPLES OF X RAY AND RADIUM DOSAGE The farther an element of volume is within a rayed medium, the greater is the amount of scattered radiation which it receives. The added component due to scatter- ing may amount to several hundred per cent of the pri- mary energy. According to measurements made by the author with the radiatio nin vogue at present (200 K V, 1 millimeter Cu., 50 centimeters focus skin distance, large port of entry) it amounts: At the surface to 50 per cent. At the depth of 5 cm to 200 per cent. At the depth of 10 cm to 350 per cent. At the depth of 15 cm to 500 per cent. At the depth of 20 cm to 700 per cent. On this account the values given by the preceding curves must all be considerably increased. If for the sake of comparison the intensity at the surface is again taken as 100 per cent, and all values reduced in the same ratio, a curve results which deviates considerably from those discussed so far. (Figure 34.) Intensity Fig: 54 077 cfepih Calculated and Observed Intensity Curves. At the beginning* it decreases less rapidly than was calculated from the inverse square law and the absorp- DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 153 tion law (Figure 33) under the assumption of the same intensity at a depth of 10 centimeters. Also farther along small discrepancies between the curves are observed, for example, if the total depth is decreased so that the radiation emerges again after penetrating 15 centimeters, the intensity in the last few layers decreases considerably. At the point of emergence it will be about one-fifth less than it was before. In general, it may be stated that by the removal of the overlying tissue, the intensity at any given point on the surface of emergence is decreased by about 20 per cent. §3. Distribution Curves, Distribution Charts. After these general considerations we may give the depth distribution for a series of treatment factors used at present. The customary factors used in deep therapy when a 200-280 K V transformer is available, are the following: 190 to 210 K V, y2 to 1 millimeter copper plus 1 millimeter aluminum, 50 centimeters focus skin distance. With large ports of entry, 20 centimeters X 20 centi- meters, or 22 centimeters diameter, the depth dose (at a depth of 10 centimeters) is 40 per cent; it can vary between 39 and 42 per cent. If smaller fields are used the depth dose decreases correspondingly. The follow- ing figure (35) gives the distribution of intensity along the central ray for the above conditions. The exact shape of the curves depends somewhat on the transformer, rectifier, the exact voltage and the filter thickness. The curves shown in Figure 35 represent the average of a series of measurements with differ- ent transformers, 200 K V and millimeters copper. The curves agree very closely with those obtained by 154 PRINCIPLES OF X RAY AND RADIUM DOSAGE Intensity Ol 0t -vl Fig" 35 crr\.depth Experimental Intensity Curves. 200 KV Max. 24 MM Cu. 50 CM F. S. D. Various Sizes of Field. Glasser in this country and Glocker and Friedrich in Germany, but deviate slightly at several points from those of Dessauer. These curves can be used for the Intensity Intensity Curve in Continuous and Discontinuous Medium: 200 KV. 24 MM Cu. 50 CM F. S.D. (20 CM)2 Size of Field. Fijf.36 cmdepth DISTRIBUTION OF ROENTGEN AND RADIUM RAYS 155 determination of the intensity along the central ray with a close approximation to the truth. The curves give the intensity for all points which lie within the rayed medium. At points where the rays leave the medium, part of the scattered radiation is lack- ing; at these points the intensity is about one-fifth less than the values given. Hence the curve in the case of a thin patient assumes the form sketched in Figure 36. Such curves are sufficient in many cases for practical dosage; they give a survey of the effect at various depths and serve as a guide in applying the desired energy. The details of their application will be described in the next chapter. 200 /C/. Cu + 1n*i Ail Ro&rftgen Ray Distribution Clurt. Erythtw* Tint Tuctor */. 00. J0c«i 7-5-Z). t \ Size of Field. [ZO cm] At boundaries of the medium, 20% of the indicated percentage must be substracted. Fig. 37A. One-third Actual Size. 156 PRINCIPLES OF X RAY AND RADIUM DOSAGE Rds£e 60a. rat. Tissue ~6ro treated Fick.63. Superposed Layers. The bag is so filled that by the application of slight pressure-it may be fitted very exactly to the outline of the support. The surface is formed by a cardboard. The thickness of the water layer is determined by inserting a stick graduated in centimeters through a hole in the cardboard. CHAPTER V Examples of Treatments § 1. Biologic facts underlying dosage. In the preceding chapters the physical and the techni- cal aids to correct dosage have been discussed. We may now take up the biologic phenomena which form the basis of dosage. A natural classification is given by the obser- vations of all investigators that very small doses are stimulating, that larger doses arrest anabolism, and that very strong doses are fatal to all tissues. Hence we may first discuss those treatments in which radium or Roentgen rays have a stimulating action on a series of biological processes. Under this head belongs the stimulation of the blood forming organs. An injection of less than 1 microcurie of radium element or the inhalation of approximately 100 emans produces a leucocytosis in a few hours. Accord- ing to Gudzent the increase in white blood cells depends only slightly on the strength of the dose. The latter was varied from 10 to 700 emans per liter, the treatment con- suming two hours daily. A leucocytosis appeared even with very small doses, with larger doses it was only slightly greater. Also short irradiations, approximately 100 e or 1/20 of an erythema dose, produce this increase, which, however, with a single application is of short dura- tion; but by continued treatments an average increase persisting for a long time can be attained. Frequently an increase of the lymphocytes and an increase in the phagocytic power of the lymphocytes can be verified. An 222 EXAMPLES OF TREATMENTS 223 increase of the red blood corpuscles is also observed when small, though somewhat larger doses than in the preced- ing cases, are given. The effect is less pronounced than the other and shows a lesser sensitivity of the red blood corpuscles as compared with the white ones. A greater increase is noted in pathologically anemic patients; in these cases doses of about 10 microcuries can bring the number of red corpuscles to normal in a few days. The increase of the red corpuscles persists longer than does that of the white. The coagulation time of the blood also is considerably shortened by the application of the above mentioned doses; the effect, however, is only tem- porary. With large doses the coagulation time is increased. All these effects seem to be produced chiefly by the action of the rays on the blood forming organs: the spleen, the bone marrow, and the lymphatic glands. These tissues are very sensitive to radium and Roentgen radiation. When injections are made the greatest con- centration of the radioactive elements is found after a few days in the spine and the spleen. The above mentioned effects of the rays on the blood and blood forming organs have led to radiation treatment of the following cases: Pernicious anemia: according to Gudzent intraven- ous or intramuscular injections, two at the most, of 0.010 milligrams of radium element at an interval of 14 days may be given. Chronic suppuration and inflammations; open sores, cuts, wounds and burns: small, stimulating doses of soft radiation are given at frequent intervals. Preoperative irradiation: By raying a short time before an operation the loss of blood can be decreased. 224 PRINCIPLES OF X RAY AND RADIUM DOSAGE For these purposes a stimulating irradiation of the spleen is recommended. A further well-known effect of small Roentgen ray and radium doses is the stimulation of metabolism; the effect on purin metabolism is especially pronounced. By an increased diuresis the uric acid content is diminished. Gas metabolism is also increased; the assimilation of oxygen and excretion of carbon dioxide is accelerated. These facts have led to radiation treatment of sub- acute and chronic articular rheumatism or gout, myalgia, and muscular rheumatism. Inhalations, injections, and oral administration are recommended. Gudzent injected soluble radium salts in doses of 0.02 milligram of radium in five intervals of 8 days. The same author administered emanation by inhalation; the concentration used varied from 11 to 130 emans per liter, a sitting lasting for 2 hours, and the total number of sittings varying from 24 to 40. The oral administration consisted of 5 portions of 3,000 to 400,000 emans daily for an average period of six weeks. Com- binations of inhalations and injections were also employed. Another effect of the rays is that on the blood pres- sure. The blood pressure, especially if pathologically increased, is lowered by stimulating doses, probably due to a stimulation of the vaso-motor nerves. On this fact is based the treatment of myocarditis, neuroses of the heart, arteriosclerosis, etc. In the case of the diseases which have just been described the curative or palliative action of the radium or X rays is one of stimulation of cells and organs to increased proliferation and function. These actions have also been observed and employed in other cases. Martius EXAMPLES OF TREATMENTS 225 observed a stimulation of the ovaries when small doses were employed, although he warns against the irradia- tion treatment of amenorrhoea, since idiosyncrasies cause large variations in dosage, and since an over-dose may easily lead to a cessation of the overian function. For the treatment of stomach ulcers stimulating doses have also been tried. Schulze Berge recommended 40% of the unit skin dose, and reported good results. Menzer employed much smaller doses, which, however, were repeated every week. These good results were confirmed by many radiologists. Also in the radiation treatment of tuberculosis we are dealing, according to most authors, with a stimulating action of the rays. On account of the low sensitivity of the tubercle bacilli to irradiation, they cannot be destroyed without harm to the surrounding tissues. Some 100 hours of exposure to beta rays coming from a full strength plaque are necessary to kill the tubercle bacilli; smaller doses, of course, do have an impairing effect on the bacilli. Various authors give various explan- ations of the action of the rays: Stephan believes in the stimulation of the proliferat- ing tissue and gives doses between 1/40 and 1/20 of a unit skin dose in cases of tuberculosis of the lungs. Hilpert also believes in stimulating doses and begins with 6% of a unit skin dose but gradually increases this to 20%. The treatments are given at intervals of 4-8 days and are continued for 6 weeks. The dose must be increased during this period because the cells become accustomed to the stimulation dose; the larger doses are not dangerous because the cells become more resistant with repeated applications. 226 PRINCIPLES OF X RAY AND RADIUM DOSAGE Holfelder also is of the opinion that the action of the Roentgen rays consists in a stimulation of the demarca- tion zone. The doses recommended by him are greater than those mentioned above. In cases of tuberculosis of the joints he recommends doses of 20% to 60% for the entire diseased region and proposes longer pauses: 8-12 weeks after the first irradiation, 12-16 weeks after the second, 6-8 months after the third, and 8-12 months after the fourth. Smaller doses are given in the last few treat- ments. He considers it of great importance that the encapsulation of the tuberculous area proceed slowly, since then the danger of a rupture of the protecting walls is lessened. Juengling and Lehmann ray the diseased region homogeneously with similar doses, 20-50% and 25-30%, respectively. Contrary to these authors, Altschul believes the action of the rays on the skin is all important and a homo- geneous irradiation with hard rays beside the point. He proposes the use of 1 mm of aluminum and in this way puts the treatment of tuberculosis into the field of super- ficial therapy. His view is that the absorption of the rays in the skin stimulates, analagous to pigmentation in heliotherapy, a sort of endocrin function of the skin, which in time acts indirectly on the tuberculous tissue. Gudzent believes that besides stimulating the connec- itve tissue the rays also take part in the destruction of the tuberculous proliferating tissue. In spite of the various assumptions as to the action of the rays, all authors agree that a stimulating action must be attained and therefore employ small doses. Nevertheless dosages of 20-60%, and more so the cumu- lative doses, are already far in excess of the doses ordi- narily assumed as stimulating. EXAMPLES OF TREATMENTS 227 Differences of opinion are found when it comes to the question of what hardness is to be used, in particular, whether hard or soft rays are the more advantageous. One thing is certain, however, namely, that very hard rays are neither requisite nor desirable in the treatment of tuberculosis. Also in the treatment of tuberculosis cutis or lupus vulgaris the Roentgen therapy is based more on a stimulating effect on the connective tissue than on a destructive action. Hence relatively small doses are given in series treatments. On account of the superficial nature of the disease rather soft rays can be used. Holzknecht uses an 8-10 inch gap, 18-25 cm. focus skin distance, 1-2 mm. aluminum filter and 4-6 H.; this is less than an erythema dose (8 H); and repeats this dose several times at intervals of 4-6 weeks. Altmann filters with 4 mm. aluminum (2.5-2.8 cm. half value layer) and gives 6-7 H., hence also less than an erythema dose (10 H.), and repeats at the customary intervals. McKee also uses doses which do not exceed the epila- tion dose at intervals of four weeks and warns against the production of a strong skin reaction. The radium treatment of lupus vulgaris is similar to Roentgen treatment when small doses and small focus distances are used. However, there is in use a beta ray method by which a superficial necrosis is produced just once. It seems that the action in this case is produced both by a destruction of the tuberculous granulation tissue as well as by the attraction of the fibroblasts by the bionecrotic tissue. Pinch, for example, uses the following radium doses: In cases of ulcerated superficial tuberculosis cutis, 1 to \]/-2 hours full strength plaque, unscreened beta rays. 228 PRINCIPLES OF X RAY AND RADIUM DOSAGE In indurated and infiltrated cases, full strength plaque, 0.1 mm lead, 2 to 3 hours beta and gamma rays. In extreme cases of long standing, full strength plaque, 2 mm lead, 20 to 30 hours gamma rays. Still more uncertain is the nature of the action of the rays in cases of vascular nevi. Pinch believes the action consists in producing proliferation of the endothelial lining of the vessels. This would mean a stimulating action and require small doses at frequent intervals. McKee is of the opinion that by radiation treatment “the mitosis is arrested, new vessels cease to form, and finally the poorly differentiated cells composing the ves- sels fail to be replaced and are absorbed.” On account of the superficial location of the vessels beta rays are employed; when too strong a dose is not to be given, slight filtration is necessary in some cases. Very pene- trating radiation, such as gamma or Roentgen radiation, does not produce favorable results and seems to affect the deeper layers unfavorably. In the following methods of treatment a more or less damaging effect is to be produced on the cells and organs. In cases of lymphatic and myologenous leukemia the object is to bring the abnormally high number of leuco- cytes down to normal. The treatment consists in raying the spleen, especially if the latter is enlarged, and the long bones, or in injecting radium salts or thorium. The radiation is best carried out with Roentgen rays, the dose may be y2 or of a unit skin dose. The use of radium applicators on the exterior is possible but imprac- tical—at least the radiation must be carried out with a number of fields, strong filtration, and large focus dis- EXAMPLES OF TREATMENTS 229 tances. Intravenously y2 mg of thorium X may be injected ; the dose depends upon the blood picture, which must be continually controlled. With this dose the num- ber of red corpuscles is usually increased. Doses which impair functions have become of consid- erable importance in gynecology. In a series of diseases the arrest of the ovarian function leads to a disappear- ance of the symptoms. To this class belong: (1) Metropathia hoemorrhagica and the hemor- rhages due to myomata. In these cases the arrest of the ovarian function arrests the hemorrhages. (2) Myomata. Roentgen or radium castration produces, like the natural climacteric, a retrogression of the tumefaction. (3) Osteomalacia. By decreasing the activity of the ovaries by means of radium or Roentgen castration the softening of the bones can be arrested. On the basis of these facts the radiation treatment of the above three diseases takes a simple course common to the three. The aim is to impair the functions of the follicles without damaging other tissues or affecting the general health of the patient. This can be done with simple means, since the ovaries are very sensitive to irradiation. A dose between l/s to y2 of a unit skin dose applied to the ovaries is sufficient to produce permanent castration. Somewhat smaller doses suffice to stop the hemorrhages. The treatment may be local if the posi- tion of the ovaries is normal or is known. In this case small Roentgen ray fields can be directed on each of the ovaries or radium may be introduced into the uterus. In 230 PRINCIPLES OF X RAY AND RADIUM DOSAGE most cases by the application of 300 mghrs, the hemor- rhages can be stopped with a single treatment. If they continue, the treatment can be repeated after a period of 2 to 4 months. The application of some 500 to 600 mghrs results in castration either at once or after one or two menstruations. More than this dose, 700 mghrs for example, are therefore not necessary for the treat- ment of myomata or osteomalacia. If by the myomata the ovaries have been displaced from their natural position and their exact location can- not be accurately determined, it is best to ray with large ports of entry. Whether the castration is carried out in one sitting or by repeated treatments used to be largely a question of technique. Nowadays castration with Roentgen rays or radium rays can conveniently be carried out in one sitting. This is desirable in cases of profuse hemor- rhages; however, it is advantageous to distribute the castration over several sittings since in this way the climacteric symptoms are greatly mitigated. Large, impairing doses play an important part in the therapy of carcinomata and sarcomata. All attempts made with small doses, just sufficient to stimulate the connective tissue, have failed. All investigators agree that doses much greater than the stimulating doses are required but there is still a difference of opinion on the magnitude of the dose. However, recent results obtained by a number of workers are gradually shedding more light on the subject. Seitz and Wintz were the first to establish a so-called carcinoma dose based on accurate physical measurements of the applied doses and careful observations of the clini- cal results. This dose is given as 100-110% of their EXAMPLES OF TREATMENTS 231 unit skin dose and is said to be the most favorable dose for effecting the disappearance of a gynecological car- cinoma (carcinoma of the uterus or breast). Kroenig and Friedrich have come to a similar conclusion. They assert that a dose 90% of their erythema dose is the most useful for the treatment of carcinoma. The erythema dose of Kroenig and Friedrich is 20-30% higher than the unit skin dose of Seitz and Wintz. Consequently the two carcinoma doses agree very well. In the practice of deep therapy the doses given gen- erally correspond fairly well with one another. With rays of weak penetration produced by apparatus of the older types a large number of fields are applied with appropriate doses, in one or more treatment series. With the hard rays available in the modern installations two methods are in use: either the so-called massive dose is given in a series of treatments over a period of a few days (Warnekross, Schmitz), or a large fraction of the dose is given at first and the rest later, a somewhat larger total energy being applied on account of the prolonga- tion of the treatment (Meyer). Recently experiments have been made with larger and with smaller doses: Perthes used doses up to 150% of the erythema dose, Juengling up to 125%, in some cases with soft rays up to 150%. Schmitz has used as high as 175% of the erythema dose in some cases to be mentioned later. On the other hand Opitz and others use doses which go down to 70 or 80% of the erythema dose. Recently attention has been called by many authors to the fact that a carcinoma dose does not exist in the sense that every carcinoma can be made to retrogress by its application. This assertion is based on the expe- rience that in spite of the application of this dose no 232 PRINCIPLES OF X RAY AND RADIUM DOSAGE improvements resulted, as well as on the observation that even after the application of the strongest doses undam- aged carcinoma cells can still be microscopically demon- strated; finally, on the fact that there are many kinds of carcinomata, which exhibit morphological, histological and genetic differences, as well as differences in their reaction to X rays and radium radiation. Thus a car- cinoma of the basal cell type reacts very readily to irradia- tion while the cylindrical epithelial cell type is much less sensitive. The so-called gynecological carcinomata (uterus and breast) are in general much easier to treat than the surgical carcinomata (stomach and rectum). Of the gynecological forms, according to Warnekross, the soft glandular types (cervix, corpus uteris, ovaries) react more easily than the hard non-glandular cancroids (vagina, vulva). There is also a difference between a primary growth and a recurrent or metastatic formation; it is well known that no other carcinomata are as sensi- tive to radiation as the skin metastases of the breast car- cinoma. According to Werner these have been made to retrogress with 30 to 50% of the unit skin dose. Finally, the result of the treatment depends a great deal on the general condition of the patient, it is a question of whether the patient can develop the necessary resistance against the carcinoma and whether or not he can over- come the toxins produced by the disintegration of the tumor. In very cachectic patients these powers are lack- ing, hence the utter hopelessness of success in these cases. The modern conception of the carcinoma dose takes account of all these factors. It is based on the experi- mental fact that for many carcinoma cases a minimum dose can be stated, below which no favorable effect can generally be expected. This minimum dose, according EXAMPLES OF TREATMENTS 233 to Juengling, in the case of the first mentioned gyneco- logical carcinomata lies between 90 and 100% of the unit skin dose; in the case of the last named carcinomata the dose is higher; in the case of skin metastases of breast carcinoma the dose it is lower. Even with these limita- tions the given value is not absolutely fixed; for example carcinomata in comparatively young people have been cured with much smaller doses, while carcinomata in senile and cachectic patients did not react favorably even with greater doses. Also in cases of laryngeal carcino- mata, according to Juengling, the minimum dose is between 90 and 100% of the unit skin dose. According to Schmitz carcinomata of the basal cell type require about 90 per cent of his somewhat higher erythema dose; this corresponds very accurately to the statements of Jueng- ling and others. According to the same author the mini- mum dose for a cylindrical epithelial carcinoma is to be found between 130 and 150% of his erythema dose, that for a carcinoma of the squamous epithelial type is still higher; Schmitz gives the value as 175%. Besides the minimum dose the maximum dose can readily be given, which the seat of the carcinoma and the adjacent tissues will endure without heavy and per- manent damage. Examples of such tolerance doses are the following: the tela subcutanea according to Jueng- ling is more sensitive than the skin, 120% of a unit skin dose is quite certain to produce a chronic endurated edema, which appears as a belated injury after some months or a year; sometimes it appears with only 100%. According to Muehlmann and Mayer the adipose tissue beneath the skin of the abdomen is very sensitive to radiation. With 150% of a unit skin dose an atrophy appears. 100% is designated as a toxic dose. 234 PRINCIPLES OF X RAY AND RADIUM DOSAGE The connective tissue and muscular tissue, according to Seitz and Wintz, tolerate very large doses, about 180%, without being greatly damaged. The mucosa of the colon and of the bladder, accord- ing to Seitz and Wintz, have a tolerance dose of about 130% of a unit skin dose. Even with less than this dose irreparable damage results; with 160% an edema and ulceration of the bladder wall occurs; with 140 and 150% ulcers of the rectum occur. The mucosa of the small intestine is less sensitive than that of the colon by about 30% of a unit skin dose. The values given for the ovaries by various authors agree very well. According to Friedrich and Kroenig, 20% of an erythema dose produces a temporary amenor- rhea. According to Seitz and Wintz, 34% produces com- plete castration; according to Warnekross, 27% produces amenorrhoea; according to Schmitz, a dose of 6 or 12% of his erythema dose is stimulating, that is, it increases the functions; 15 to 22% decreases the functions, 25% to 40% is the castration dose. The following doses for the testicles are stated by Schinz: above 34% oligonecrospermia occurs; with 60% total aspermatogenesis and azospermia; above 60% total castration. For the treatment of carcinomata of the stomach a recent publication by Holfelder and Peiper is very sig- nificant. According to their investigations the cortex of the suprarenal glands is very sensitive to radiation, with as high as 60% of a unit skin dose no irreparable dam- age of the suprarenal glands of guinea pigs appears; larger doses more or less destroy the cortex, the lipoid content rapidly decreases and the animals die. In the human subject 100-110% of a unit skin dose produces EXAMPLES OF TREATMENTS 235 great damages, Addison’s pigmentation and malaise for some months. In some cases after strong irradiation Addison’s disease with fatal results occurs. Tyler has called attention to the danger involved in intensive irradiation of the lungs. He observed fibrous changes following deep therapy treatment of breast and lung carcinomata. Pfahler states that there are two pos- sibilities: (1) A malignant process becomes transformed into fibrous tissue under the influence of the irradiation. (2) An original fibrous process is stimulated to further growth. A recent article by Juengling deals with carcinoma of the larynx. While irradiation with 100-120% of a unit skin dose, even if repeated after a period of one or three months, did not produce any particularly early reactions (three days) or normal reactions (three weeks), there did appear in a very large number of cases irreparable belated damage after 6, 12 or even 15 months which resulted in telangiectasies, sloughing, impossible deglutition, and finally death. At this stage an operation was no longer possible since there were adhesions to the adjacent tissues and cirrhoses. According to these authors therefore no dose stronger than 100% should be given and this dose cannot be repeated before three months have elapsed. Three irradiations can never be carried out. Also, according to Lehmann, with 110% the larynx can become gangrenous. Similar danger of belated damages, according to both Juengling and Lehmann exists in joint cases. Larger doses than those absolutely necessary should not be given if belated effects are to be prevented. The doses when- ever possible (tuberculous cases) should stay below 50%. The bony tissue, according to Seitz and Wintz, and 236 PRINCIPLES OF X RAY AND RADIUM DOSAGE many other authors, tolerates very large doses; cartilage is more sensitive. The periosteum is easily damaged by a destruction of its blood vessels. Changes produced in the blood are more dependent on the total applied energy than on the energy density at any one point. Accordingly, a statement of the exact dose is difficult. In the case of intensive irradiation the number of the white as well as the number of the red corpuscles decreases greatly; the white corpuscles may almost entirely disappear after almost fatal doses have been applied. The coagulation time of the blood is decreased by the application of small doses; by the appli- cation of large doses it is considerably increased. Levin states that the lymphocytes are the most sensitive cells in the animal organism. Only when these are not dam- aged, a new formation of connective tissue, which is so important for the reception and displacement of malig- nant tissue, takes place. The blood forming organs, the spleen, the bone, and the lymphatic glands are known to be very sensitive to large doses of Roentgen rays. Heinecke states that the lymphatic system is more affected by radiation than any other tissue; however, these organs regenerate relatively well, if the damage, either acute or chronic, does not exceed a certain limit. According to Altmann and Wetterer, the various tis- sues may be placed in the following order of decreasing radio-sensitivity: 1. Normal tissue: Lymphatic tissue, testicles, and ovaries. Pathological tissue: Leukemia, pseudoleukemia, psoriasic patches of recent origin, acute eczema. EXAMPLES OF TREATMENTS 237 2. Normal tissue: The skin of the face in children, cartilage in children, mucous membrane. Pathological tissue: Chronic eczema, mycosis fungoides, lymphosarcoma, acne vulgaris, old psoriasic patches, lupus hypotrophicus, tuberculous lymphomata. 3. Skin, sudoriferous glands, sebaceous glands. 4. Connective tissue, muscle cartilage, bone. According to Ewing the radio-sensitivity of the (malignant) neoplasms may be tabulated as follows in the order of decreasing sensitivity: Lymphomatous group: Cellular type of Hodgkin’s disease, Leukemia, Lmyphosarcoma, Thymic ulcers, Myeloma; Cellular carcinoma, anaplastic carcinoma, malignant carcinoma; Myeloma, angioma, adenoma, adeno-carcinoma; Basal cell carcinoma; Hornifying squamous carcinoma; The neurofibrosarcoma is the least sensitive. The following table, taken from the same author, covers some of the structures of ectoplasmic origin: Bladder mucosa, Rectal mucosa, Buccal mucosa, Skin, Brain tissue. The latter is almost non-sensitive to irradiation. 238 PRINCIPLES OF X RAY AND RADIUM DOSAGE On the basis of these facts a lower and an upper limit may be given for a number of defined carcinomata. According to Caspari and others the lower limit is fixed by the condition that the carcinoma is damaged and that the power of resistance of the body is both locally and generally mobilized. Caspari states that for this purpose a weak necrosis is necessary; this acts as a powerful stimulant on the fibroblasts, which by their proliferation continue the destruction in the tumor. The necrosis must not be so large that the resulting toxic effects per- manently injure the organism. These conditions fix both the lower and the upper limit of the dose and determine an optimum carcinoma dose for a particular case (not the carcinoma dose in general. Its range may vary con- siderably. For an individual whose power of resistance is great a slight necrosis is sufficient to mobilize the fibro- blasts ; the body can also endure a much greater necrosis. On the other hand, a patient whose power of resistance is low requires a larger dose to stimulate the fibroblasts, but the general injurious effect produced is too great to be repaired by the body. This explains the ineffective- ness of Roentgen treatment in the case of highly cachec- tic patients. The carcinoma dose for a basal cervix carcinoma exhibits a wide range. It begins with 90% of the unit skin dose; only with as high as 120 or 130% need damage of the surrounding organs be feared. Hence by a homo- geneous irradiation of the pelvis with a dose lying in this range, favorable results may be produced in non- cachectic cases. By the use of heterogeneous radiation much larger doses can be applied locally. Many thou- sand mghrs of radium can be applied through the cervi- cal canal and a very heavy necrosis can be produced at EXAMPLES OF TREATMENTS 239 the focus of the carcinoma without seriously injuring the surrounding tissues. Hence even a cervix carcinoma of the cylindrical cell type can be successfully treated. The range of the dose in this case is not so large on account of the high minimum value of the dose. In the case of an epithelioma of the skin, in spite of the high minimum dose, a carcinoma dose of wide lati- tude can be given since by the use of soft rays a small region of the skin can be rayed superficially very intensely without any danger to the underlying tissue or surrounding skin. The range of the dose in the case of carcinoma of the larynx is very narrow according to recent researches. Nearly in every case 90% of the unit skin dose is neces- sary; 100% represents the upper limit. Since the range is so narrow, care must be taken to attain a good degree of homogeneity in the rayed region; otherwise some parts will receive too much and others too little. Carcinoma of the stomach is also difficult to treat on account of the small range of the permissible dose, deter- mined by the great sensitivity of the endocrine glands and the pancreas. These few examples serve to illustrate what extremely different forms the problem of correct dosage may take for different cases. They show that a carcinoma dose does not exist. There can be no fixed procedure employing any one method of irradiation (Roentgen rays only, radium rays only, homogeneous irradiation, large fields* small fields). It is only by the correct combination of these means in a given case that all the difficulties can be overcome. 240 PRINCIPLES OF X RAY AND RADIUM DOSAGE A discussion of the contraindications of irradiations is beyond the scope of this book. The conditions in the case of sarcoma are still more complicated than those just discussed in the case of car- cinoma. Seitz and Wintz state the sarcoma dose as 60 to 70% of the unit skin dose. Kroenig and Friedrich determine the sarcoma dose as 50% of their erythema dose, hence practically the same dose. These values are very likely correct for sarcomata of the small round cell type and for sarcomata of the lymphatic system. They certainly do not hold for giant cell sarcomata and sarcomata of the bones. According to Morson the following gradations in sensibility and reactions may be distinguished: Spindle cell sarcomata are amenable to treatment if not growing in bone tissue; Periostial and endostial sarcomata are more resistant; Chronic sarcomata are sometimes improved; With melanotic sarcomata the results are unfavor- able. Schmitz is of the opinion that: Small round cell sarcomata require approximately 70%; Small spindle cell and mixed cell sarcomata approximately 130%; Large spindle cell sarcomata approximately 175% ; Giant cell sarcomata approximately 200%; Lympho-adenoma, pseudo-leukemic lymphnodes, according to Schmitz, require about 30% of his erythema dose. In his most recent articles Juengling calls attention to several important points: EXAMPLES OF TREATMENTS 241 The sarcoma doses are even more indefinite than the carcinoma doses; even apparently similar types react very differently to the same treatment. Furthermore, the range of the favorable dose is remarkable; with very small and with large doses the same effects appear. Wintz also has recently called attention to this range of reaction. A prolongation of the dose matters much less according to Juengling in the case of sarcoma than it does with other malignancies. The prognosis is not as unfavorable in the case of cachectic patients for sarcoma than for carcinoma. The effect seems to depend very little on the general condi- tion of the patient. On the other hand, with sarcomata much greater danger of metastases exists than with carcinomata; hence a more careful irradiation of the lymph vessels is necessary. Juengling states that in general a sarcoma dose is much less determined than a carcinoma dose even when all the factors which determine the dose are taken into account. Lethal doses are never employed in deep therapy, if a lethal dose is defined as one which produces death of the entire organism. Bacteria in general are very resistant and would require doses so great that the surrounding tissue would be totally destroyed. However, it is important to have a knowledge of the doses which can damage the entire body or which can result in death. Of course all statements are very unac- curate since they can not take account of the many vari- 242 PRINCIPLES OF X RAY AND RADIUM DOSAGE able biological factors, such as the region of application, the constitution of the patient, etc. Wintz states that 6 or 7 a, that is, the application of 6 or 7 fields of the kind previously discussed produces a long continued injury to the patient. The ports of entry which are used in his technique are small, they amount to 48 sq. cm. (6 cm. X 8 cm.). Besides the pene- trating power of the rays used is not great; only about 18% of the energy applied to the surface reaches a depth of 10 cm. With a field of this type about 1.5 X 10® e are applied. Since 6 or 7 fields are used, altogether as much energy as with a large field is applied, namely, about 107 e. Treatment of the uterus by means of three large fields or two large and two small fields supplies about three times this energy. The same total dose is there- fore applied at one time, which in the Seitz and Wintz technique would be given in three series. Such an inten- sive irradiation is not easily endured on account of the large supply of energy. Hence the author recommends: 1) a procedure which applies a minimum of total energy; 2) a distribution of the treatment series over a period of one week, and 3) the previously mentioned means to reduce the radiation sickness. Somewhat larger total doses fall into the range of the doses dangerous to life. The author is of the opinion that the application of more than four large fields in cases of extended carcinoma or general carcinomatosis imperils life in the majority of cases and therefore of necessity advises the distribution of the dose over sev- EXAMPLES OF TREATMENTS 243 eral series. Numerically the mentioned maximum dose which in some cases could be a fatal dose can be given as 5 X 107 e. Of course, a necrosis with fatal results can be produced by a much smaller dose if it is highly con- centrated. We are not concerned with these cases here. The fatal dose of gamma radiation was investigated experimentally on animals by Lazarus and Barlow. They found that the gamma rays of 5 gram of radium element applied for 6 hrs. to a rat so injured the animal that it died in 42 hours. The corresponding time for rabbits was 9 to 10 hours. From these experiments no conclusions as to the corresponding dose for man can be drawn, first, on account of the great difference in size, and secondly, on account of the greater sensibility of man to Roentgen and radium rays. The author knows of a case where a 10 mg radium needle applied for 7 days, that is, an appli- cation of 1700 mghrs of beta and gamma rays, produced death of the patient inside of 7 days. This result, how- ever, was caused less by the general action of the rays than by the terrible necrosis produced in the immediate neighborhood (2 cm radius) and by the severe inflam- mation of the adjacent tissue (7 cm radius) in the abdomen. If the needles are properly distributed, a dose of 1700 mghrs can be given without danger. In the application of unfiltered emanation tubes which are to remain in the tumor Failla recommends a quantity no larger than 4 millicuries. This corresponds to an appli- cation of 533 mghrs. For larger tumors the dose should be about 0.5 millicuries per ccm. It is assumed that no large blood vessels or particularly sensitive organs are in the immediate neighborhood. Failla has also given permissible doses for injection of solutions of radioactive 244 PRINCIPLES OF X RAY AND RADIUM DOSAGE substances (active deposit dissolved in physiological salt solution) into the veins or into the tumor. According to Failla it is advisable not to exceed 200 micrograms of radium element in 2 to 6 ccm of solution. With 250 micrograms severe toxic symptoms appear. Gudzent states that doses of 500 micrograms of radium element and of one milligram of thorium X are close to a danger point. On the other hand Cameron, Viol and Proescher have administered intravenously up to 5 mg of radium bromide, that is, 2.7 mg of radium ele- ment in 2 ccm of normal salt solution without observing any bad effects; they consider, however, 50 to 100 micro- grams of radium element as the correct and safe dose. § 2. Methods of treatment. The preceding discussions give an idea of the size of the dose that is necessary in the majority of cases for relief or cure. Up to this point the problem of dosage has been largely biological or medicinal since it is impor- tant to know the location and extent of the diseased tis- sue, the nature of the disease, and the constitution of the patient. Once this is known the necessary step is to determine the best, that is, the least harmful and most economical method, which applies the correct dose in the specific case. The possibilities of the applications are legion as has been seen in the preceding chapter. Since a variety of methods are available: Roentgen or radium rays, soft as well as hard, to be applied locally or gen- erally, or radioactive materials to be administered into the blood, by mouth or through the lungs. In order to find the correct method of treatment it is necessary to pay special attention to three conditions: EXAMPLES OF TREATMENTS 245 1) The location of the region to be rayed: it may be superficial, central, or at a small depth within the tissue. The different locations require very different treatment and for each of the three possibilities a different method is appropriate. 2) The extent of the region to be treated: it may be localized, it may involve a large but bounded volume, or it may involve the entire body. The question whether local or homogeneous irradiation is required or whether a general treatment is necessary is decided by these con- ditions. 3) The magnitude of the dose. In the choice of a treatment technique it is very important to know whether small or large doses ought to be applied. In some cases the magnitude of the dose is limited by the available technique so that only an approximation of the correct dose is possible. In the following, on the basis of these physical view points, the determination of the possible methods of irradiation is carried out for a number of cases occurring in practice: (a) The conditions are simplest when a superficial region is to be rayed. Of course only soft rays are to be considered. Unfiltered rays or rays filtered with 1 mm of aluminum produced with a 20-25 cm (a 8-10 inch) spark gap, that is, about 60 to 80 K V, and with 20 to 25 cm focus skin distance. Only in cases where the infection extends to deeper layers a filtration of about 4 mm of aluminum is necessary. In radium treatment chiefly beta rays are used. For this purpose unfiltered surface applicators placed directly on the skin are most 2 46 PRINCIPLES OF X RAY AND RADIUM DOSAGE suitable. For processes involving deeper layers small filtration and distances from a few millimeters up to 1 cm are appropriate. In this case an appropriate surface applicator can be made out of several radium needles. Particularly superficial diseases react better to unfiltered radium radiation since the latter delivers the least pene- trating radiation. Lupus erythematosis belongs to this class, a disease which is not easily affected by Roentgen or gamma radiation but which responds very well to beta radiation. The conditions are the same for vascular nevi; in the treatment of the latter beta rays produce good results while Roentgen and gamma rays fail. In cases of nevus flammeus even beta radiation is too penetrating so that ultra violet rays or perhaps alpha radiation would be more favorable. However, in case of angioma caver- nosum where the deeper vessels are involved, the some- what harder gamma radiation of radium or Roentgen radiation is more effective. In a number of dermatoses soft Roentgen radiation must be used, first, because the seat of the disease is in the superficial layers, and, secondly, because the disease frequently involves large surfaces. If the radiation were carried out with penetrating rays the deeper lying organs (blood, bone marrow, and spleen) would be exposed too much and injuries to the whole organism would be pos- sible. In this category belong such dermatoses as psori- asis, eczema and lichen rubra. Ephitheliomata in their early stages can also be treated with soft Roentgen rays or with beta rays, particularly the squamous and cylin- drical cell types which require very large doses. By limit- ing the field to the affected area and by not raying too deeply it is possible to give local massive doses without any danger of doing any damage. EXAMPLES OF TREATMENTS 247 In cases of deeper infiltration (epitheliomata of a pavement or tubular epithelial origin) of course, heavily- filtered Roentgen radiation or gamma radiation of radium, applied from a distance of a few centimeters is appropriate. A number of diseases which have their seat at the hair follicles or in the deeper corium layers may also be treated with somewhat more strongly fil- tered radiation. For this class belong the dermatomy- coses: trichophytosis, favus, tinea tonsurans. Acme vul- garis also must be treated with radiation filtered through about 4 mm. of aluminum, since the sebaceous glands are located at a depth of a few millimeters. The doses to be used in superficial therapy range between the small doses, 1/10 of the normal skin dose or more, applied fractionally, in cases of eczema, psoriasis, keloids, mycosis, fungoides, chronic ulcers, etc., to large doses which are given in a few applications in cases of favus, verruca, clavus and epithelioma. In case of epi- thelioma a dose as high as 2 or 3 times the unit skin dose can be given, and this dose may even be repeated in two to four weeks. An excellent summary of a well developed technique of Roentgen therapy has recently been published by Holzknecht in the form of a dosage table. While Holz- knecht’s deep therapy technique does not correspond to that employed in the United States since lower voltages, less filtration, and small focus skin distances are used, his superficial therapy technique is very similar to that in vogue in this country. The table gives a schematic but extremely useful outline of the most important treat- ment factors. In the following it is reproduced in a somewhat different form imposed by the lack of space. 248 PRINCIPLES OF X RAY AND RADIUM DOSAGE Condition gap cm FSD cm H AL mm Series- Interval Weeks Number of Series Unit Skin Dose H Group Epithelioma \ Verruca, Clavus / 27 18-35 8-15 3-4 4-8 1-2 9 I Acne vulgaris 27 18-25 6 3-4 1-2 1-5 9 II Bubo 27 18-25 6-8 3-4 2 1-2 Condulomata acumi- nata 27 18-25 6-8 3-4 6-12 1-3 Hyperhydrosis con- tinua 27 18-25 6-8 3-4 6-12 2-3 Hypertrichosis 27 18-25 6-8 3-4 12-16 3-5 Carbuncle 27 18-25 6-8 3-4 1 Rhino scleroma 27 18-25 6-8 3-4 6-12 1-5 Keloid 27 18-25 6-8 3-4 6-12 1-5 Pseudoleukemia 27 18-25 6-8 3-4 6-12 1-5 Tuberculous lymph- oma 27 18-25 5-7 3-4 6-12 1-5 Glandular tubercu- losis 27 18-25 5-7 3-4 6-12 1-5 Tuberculous sinovitis. . 27 18-25 5-7 3-4 6-12 1-5 Alopecia areata 20-25 18-25 4-6 1-2 1 7 III Congelation 20-25 18-25 4-6 1-2 4-6 1-2 Erythema enduratum. . 20-25 18-25 4-6 1-2 4-6 1-5 Favus 20-25 18-25 4-6 1-2 1 Furunculosis 20-25 18-25 4-6 1-2 4-6 1-5 Herpes tonsurans... 20-25 18-25 4-6 1-2 1 Lupus vulgaris 20-25 18-25 4-6 1-2 4-6 1-5 Mykosls fungoides.. 20-25 18-25 4-6 1-2 4-6 1-5 Phlegmons 20-25 18-25 4-6 1-2 4-6 1-5 Scrophuloderm 20-25 18-25 4-6 1-2 4-6 1-5 Congenital stridor.... 20-25 18-25 4-6 1-2 4-6 1-5 Trichophytosis 20-25 18-25 4-6 1-2 1 Tuberculosis of the mucosa 20-25 18-25 4-6 1-2 4-6 1-5 Lupus excdens 20-25 18-25 4-6 1-2 4-6 1-5 Dermatitis capillaris capillitii 20-25 18-40 3 1 2-3 1-2 5 IV Chronic eczema 20-25 18-40 2-3 05-1 2-3 1-2 Lichen planus 20-25 18-40 2-3 05-1 2-3 1-2 Pityriasis rosea 20-25 18-40 2-3 05-1 2-3 1-2 Pruritus 20-25 18-40 2-3 05-1 2-3 1-2 Psoriasis 20-25 18-40 2-3 05-1 2-3 1-2 Column 1 gives the disease to be treated. Heavy type denotes those in which Roentgen irradiation is, at the present stage of the science, the treatment of choice . . . ; those which experience has shown to be very favorably affected by X ray are shown in italics . . . ; ordinary EXAMPLES OF TREATMENTS 249 type denotes those in which Roentgen treatment has given favorable indications although other methods of treatment may be used. . . . Column 2 gives the voltage in terms of the spark gap in centimeters between points. Column 3 gives the focus skin distance in centimeters. When extensive irradiation becomes necessary as in the last group (IV), larger focus skin distances are some- times necessary to insure surface homogeneity; accord- ing to Holzknecht the distance should be double the size of the field if a plane surface is to be uniformly rayed from a single point. In the irradiation of very large sur- faces, of the head in particular, so-called total irradia- tions in which boundaries of the field are not fixed by absorbing materials become necessary and the focus dis- tance can be somewhat smaller. Column 4 gives an idea of the energy to be applied at the surface. In the first and second groups, that is, with fairly strongly filtered radiation, 9 H corresponds to a unit skin dose. In the third group (1-2 mm Al) 7 H corresponds to the same dose. In the last group the unit skin dose can be assumed equal to 5 H. The H values give the size of the single dose, the effect of vary- ing hardness being taken into account. Column 5 gives the interval between two treatment series. Holzknecht states that six weeks are required for the recovery of the epithelium when an erythema dose has been applied. When more than two series have been administered, the recovery of the capillaries must also be considered; this requires some three months, if belated effects such as atrophy of the skin, telangectasies. and ulceration are to be avoided. If very soft radiation is 250 PRINCIPLES OF X RAY AND RADIUM DOSAGE used, the periods between series may be of shorter duration. Column 7 gives the number of series to be applied. The number of series should not be too large; the first series produces the major part of the results; additional series, after a certain limit has been reached, is apt to be more harmful than beneficial. One series may be given as a precautionary measure after the cure of the disease has been effected. We are concerned here with treat- ment series, not single treatments, because in extensive dermatoses several fields must be used and also because the treatment of a single field may be extended over sev- eral sittings. The basic idea of the table is the classification of the diseases into four groups, which are to be treated with doses of different strengths and with radiations of differ- ent degrees of hardness. These two factors: dose and hardness, i.e., quantity and quality, determine to a great extent both the time intervals between series and the number of series, so that only a small variation in these factors is to be expected. (b) The second physical group consists of those cases in which the diseased area is situated at a depth. The technique used in these cases is radically different from that used in the superficial group: it is characterized by the use of very hard rays applied through several ports of entry. Frequently radium may be used in addition, or alone. The development of deep Roentgen therapy began with the application of many small fields which were concentrated on the region to be rayed. This method was worked out chiefly by Seitz and Wintz in the Frauen- klinik at Erlangen. The large field method, which con- EXAMPLES OF TREATMENTS 251 sisted chiefly in the application of four fields to cases of extended carcinoma of the uterus, was developed by Des- sauer and Warnekross on the basis of the phenomena of scattered radiation. For a time these two schools opposed one another, and each one emphasized the advan- tages of their method. Recently, however, each method has found its own field of application depending on whether a localized or a homogeneous effect is desired. In fact it is an important question whether a very limited volume is to be given a large dose or whether an extended volume is to be treated with a smaller dose distributed as uniformly as possible. From the standpoint of the local or homogeneous treatment a few examples of deep X ray therapy will now be considered: Seitz and Wintz in the development of the cross fire method considered the treatment of uterine carcinomata under the head of localized treatment. Next when they found that the broad ligaments required an irradiation equally as strong as the primary carcinomata in order to cure or prevent recurrent carcinoma, they added a local- ized treatment of the parametral regions. The treatment factors of Seitz and Wintz were 170 K V, 2-3 M A, 0.5 mm zinc filtration, 23 cm focus skin distance, 6 cm X 8 cm port of entry or an anatomi- cal cone, a quadrant of about 100 sq cm in area. With these factors the depth dose was 18%. With the appli- cation of a unit skin dose to the skin, the use of 6 or 7 fields, and with the aid of compression, a Seitz and Wintz carcinoma dose could be applied to the interior. Com- pression is practical when small fields are used, especially in the region of the abdomen; it shortens the path of the rays by several centimeters and makes the tissues blood- less. With large fields compression has little effect, since 252 PRINCIPLES OF X RAY AND RADIUM DOSAGE it displaces the part to be rayed. An irradiation of the parametral regions if necessary is carried out later: After a period of 6 weeks three ventral fields and three dorsal fields similar to those used in the uterus treatment are employed and the radiation concentrated on the right parametrium; after another interval of 8 weeks the left parametrium is treated. The advantages of this method are, that it spares the patient, that in one series only a comparatively small volume of tissue and blood is rayed, and that between the series the patient is given a long time for reaction and recovery. The difficulties involved in this method are that the path of the beam and the extent of the region subjected to the rays must be known very accurately and that a great deal of skill is required to concentrate the rays correctly on the desired region. The disadvantages are, perhaps, that portions of the can- cer tissue are left for some time without being treated and that other parts do not receive a sufficient dose. However, in the light of our present knowledge these points will not cause a great deal of anxiety. The accu- rate determination of the energy distribution in the inte- rior when this method is used is not easy. The distribu- tion depends to a high degree on variable factors, in par- ticular on the distance between adjacent fields. In general the action of as many as six or seven fields is not as localized as one is inclined to believe. In particu- lar due to an overlapping of the beam, areas of high energy concentration may easily occur outside of the region to be rayed. In the treatment of the uterus Seitz and Wintz have also enlisted the aid of radium, insuring an increased localized action on the focus of the carcinoma. The sterilization of the ovaries in hemorrhages, myo- EXAMPLES OF TREATMENTS 253 mata, osteomalacia is often carried out with small fields or by the application of radium through the uterind cavity. This method is always appropriate when the exact location of the ovaries is known and their distance from the radium source is not too great. The treatment is not difficult since only small doses are required. While in these cases localized irradiation has been fre- quently displaced by homogeneous irradiation, in other cases the former has proved its superiority. This is true for example, for many cases of carcinoma of the stomach. According to Holfelder and Peiper the organs adjacent to the stomach are very radiosensitive. The suprarenal glands and the spleen can endure only small doses without damage. A strong irradiation of these glands as well as of the pancreas and the liver would result in aggravating the radiation sickness, which, however, is to be avoided in the treatment of the stomach. Homogeneous irradiation of the region of the stomach has been frequently carried out, but in general without prompt results and with serious injury to the patient; local irradiation by means of very carefully selected small fields insures (according to Holfelder’s experience) much better results. Holfelder states that all the fields cannot be given at right angles to the axis of the body. The best arrangement is that illustrated by the following diagram (Figure 60). The field which supplies the greatest intensity is best given obliquely from below to the affected part of the stomach, its prolongation then neither strikes the spleen nor the suprarenal glands. Often two other fields with a very favorable depth dose can be given from the left and right side, at right angles to the axis of the body and as close to the front as possible. A less effective dorsal 254 PRINCIPLES OF X RAY AND RADIUM DOSAGE field can be given from above through the lower part of the lungs. All fields then lie in an oblique section through the body, the plane of which passes anteriorly below the Su.^rarz'nals JPjlamjC /kid Sb^ SfUett Co &'ll pancreas. Fi(k. bo. Oblique Ports of Entry in Treatment of the Stomach. stomach and posteriorly above the stomach. The distri- bution in this plane can be easily determined with the help of the charts. Figure 61 exhibits the results, which were obtained by the method previously discussed. The anterior-poste- rior diameter appears elongated because the cross-sec- tion passes obliquely through the body. For the same reason the section passes through the lungs at the rear, through the stomach and the liver at the center, and pos- EXAMPLES OF TREATMENTS 255 sibly through the colon in front. The irradiation is car- ried out with 4 fields of the type previously discussed; each field is about 10 cm X 10 cm and light compression is used. The skin dose is reduced to a total of 100%. The intensity corresponding t o4 points has been calculated. The values show that three fields alone supply sufficient Co Low Stomach Liver & 1- . Cross Section of Patient, Treatment of Stomach, 4 Ports of Entry. 200 KV. Y MM Cu. 50 CM F. S. D. intensity to the greater curvature of the stomach; it is more difficult to supply enough energy to the more centrally located regions (lesser curvature). Even with 4 fields the intensity is still insufficient; however, another 256 PRINCIPLES OF X RAY AND RADIUM DOSAGE field applied from the front may be added to make up the necessary energy. The irradiation of stomach ulcers can be carried out similarly except that much smaller doses are required; so that two fields per series and a low skin dose are sufficient. In cases of cancer of the oesophagus fields at right angles can be employed since the beams do not strike very susceptible organs. A localized treatment with small fields should be carried out in order that too great an amount of energy is not applied to the lungs. In cases of cancer of the oesophagus combined Roentgen ray and radium treatment is often favorable. A further application of localized irradiation is found in the tumors of the hypophysis. On account of its central location in the head, the hypophysis can easily be reached from various ports of entry. In addition, radium can be applied through the nose. Carcinomata of the bladder, of the rectum and of the prostate are often treated locally by means of radium. The following possibilities of radium application exist: (1) A capillary tube may be placed in the center of the bladder distended with water, or in the center of the rectum. In the latter case the radium capsule may be surrounded by an amber or bakelite sheath in order to secure its central position. A total of 1,000 milligram- hours applied in fractional doses may be used. This method makes a fairly uniform irradiation of the entire inner wall possible, with some penetration. (2) Lightly filtered or unfiltered preparations may be applied locally to the affected region. Strong reactions may be produced at the surface, some 500 milligram- hours being applied. (3) The tumor can be made accessible by means of EXAMPLES OF TREATMENTS 257 an operation and the needles or emanation tubes can be inserted directly into the tumor. In contrast to localized irradiation let us consider the homogeneous irradiation of extended regions. The lat- ter method must be used in cases of carcinomata of abdo- minal organs, particularly of the uterus and adnexa, as well as in metastases in the liver; the entire liver should receive a homogeneous irradiation if in any way possible. The advantages of homogeneous irradiation are as follows: (a) Uterus carcinomata, especially cervix carcino- mata spread laterally very rapidly to the parametric regions and upward along the lymph vessels to the liver. Hence it is very appropriate to ray the entire environ- ment of the primarily involved region or, as the case demands, to ray the entire pelvis and the lymph vessels, as high up as the umbilicus. (b) The organs lying in the region to be rayed in this case are not so sensitive that the correct application of the required dose involves any danger. (c) With large fields the required dose can be applied with a greater degree of accuracy than was the case for small fields; overexposure produced by overlapping of the beams or underexposure produced by erroneous localization or by an inadequate aiming of the beams, can more easily be avoided. The large field method at the present time emplo"15 the following treatment factors: 200 K V; ]/2-1 mm of copper; 30-60 cm focus skin distance; 100 sq cm-400 sq cm size of field; 2, 3, or 4 large fields. 258 PRINCIPLES OF X RAY AND RADIUM DOSAGE When two fields are used one is applied anteriorly and the other posteriorly, each being 20 cm X 20 cm; when three fields are used one large field is given ante- riorly and two obliquely from the dorsal side; when 4 fields are used two large square fields are given one ante- riorly, one posteriorly, and two rectangular lateral fields are given at right angles to the others. The most homo- geneous distribution is obtained in the last case. This is shown by the following illustrative cases: <=% il fz Uctot^C Distribution Obtained with 2 Ports of Entry, Anterior, Posterior (Abdomen). 200 KV. yi MM Cu. 50 CM F. S. D. Figure 62 shows the isodosage lines in a cross section of the body. If an energy of 100% is applied to the sur- face in the case of the two large fields the interior receives EXAMPLES OF TREATMENTS 259 about 72%, in general therefore an insufficient dose. The region of the broad ligaments receives only about 70%. Laterally, the energy decreases very rapidly. fa OctZuil Distribution Obtained with 4 Ports of Entry, Rectangulary (Abdomen). 200 KV. MM Cu. 50 CM F. S. D. Figure 63 shows the distribution obtained with 4 fields; it is almost homogeneous. At every port of entry the intensity increases slightly during the first few centi- meters, in the interior, the intensity decreases to 95%; hence an intensity sufficient for most cases is produced in the interior. While in the case just discussed the fields were at right angles (anterior, posterior, right, left), another 260 PRINCIPLES OF X RAY AND RADIUM DOSAGE arrangement often employed with smaller fields, 10 X 10 cm, is shown in Figure 64. t°4- Distribution Obtained with 4 Small Ports of Entry and Compression (Abddmen). 200 KV. 24 MM Cu. 50 CM F. S. D. The beams pass obliquely through the body, the fields being applied anteriorly and posteriorly. By means of compression the distance is decreased by 1 or 2 centi- meters, the rays are not directed at the cervix but toward the broad ligaments. The distribution is less homogen- eous than in the preceding case, the cervix received 107%, the broad ligaments only 95%, and the vicinity of the bladder 120%. Surprising results are often obtained as shown in this particular instance—the extreme heterogeneity found in this case would hardly be anticipated. If all the central EXAMPLES OF TREATMENTS 261 rays are directed toward the cervix, the distribution becomes still more heterogeneous. Another possible arrangement for treating the abdo- men is shown in Figure 65. Three Medium Sized Fields (Abdomen). 200 KV. 24 MM Cu. 50 CM F. S. D. Three medium sized fields are applied at such angles that the central rays make nearly equal angles (120°) with each other. If the patient is thin, approximately 100% is supplied to points in the interior. However, due to lack of compression it is not possible to attain a very 262 PRINCIPLES OF X RAY AND RADIUM DOSAGE uniform distribution, sometimes an overexposure of the vulva results. This method give a distribution well suited for the treatment of cancers of the vagina, of the prostate, and deep seated carcinomata of the rectum. In cases of carcinomata well up in the rectum the treat- ment is best carried out with 4 fields. The combination of radium and Roentgen radiation is often advisable, particularly in the following cases: (a) When the patient is very thick so that it is diffi- cult to produce sufficient intensity in the interior. (b) When the cancer is of such a type (cylindrical cell carcinoma), that it is desirable to apply a larger dos- age locally than the surrounding organs can endure. In both these cases the dose is limited to the maximum dose tolerated by the bladder and the rectum. In estimating the relative magnitudes of the doses to be applied, two facts must be kept in mind. First, if a relatively strong radium dose or radium alone is applied, the local reaction of the cervix or uterus predominates; and, second, with a relatively large Roentgen dose the greatest homogeneity is in the region of the broad liga- ments. If radium alone were used, the broad ligaments in most cases would not receive sufficient energy, since they are at a much larger distance from the source than the bladder or the rectum. The maximum dose, if radium alone is applied, is from 4000-5000 mghrs when the dis- tance of the source from the bladder and rectum is 1 inch. Only in cases of strong infiltrating carcinomata of the cervix where the distance to the bladder and rectum is great, can larger doses be given. In extremely unfavor- able cases the bladder and rectum can be partially shielded by means of protective lead screens some 3 mm in thick- ness. EXAMPLES OF TREATMENTS 263 Roentgen and radium radiation should never be applied simultaneously. One reason is that the radium capsule screens a part of the region to be rayed in one direction and sends out secondary rays in the other. Under- or over-exposure can easily result. A second reason is that the simultaneous combination of several large Roentgen ray fields and radium treatment is more than the patient can withstand. A distribution of the dose over a period of time is better than a concentrated irradiation from the standpoint of the general effect on the patient. The accurate dosage necessary in cases of carcinoma of the uterus requires individual treatment and a very careful estimation, either by measurement or from dis- tribution charts, of the Roentgen or radium energy to be applied. In order to facilitate this procedure an attempt has been made in the following table to give a simple scheme for the irradiation of this organ. The table provides for combined Roentgen and radium treatment, it gives the number of fields and the number of milligram-hours as a function of the anterior-posterior diameter of the patient. Two possibilities are left open to choice: The greater part of the energy may be applied by means of Roentgen radiation and a small amount of radium energy added, or the major portion of the energy may be applied with radium and a small amount of Roent- gen radiation added. The first method is advisable when the carcinoma has been cut away and the broad ligaments and lymph channels require large doses; the second method is to be preferred in cases of beginning carcino- mata or of epitheliomata of the cervix, when a strong local action is desired at the focus of the tumor. In cases of extensive involvement of the cervix (cauliflower 264 PRINCIPLES OF X RAY AND RADIUM DOSAGE growths) it is advisable to distribute the dose over the tumor by imbedding needles or emanation tubes. Anterior- X rays, Time reduc- Radium, 1*4 mm Posterior number tion for Diameter of fields each field brass filtration 10 cm 2 30% 0-1000 mghrs 15 cm 2 18% 1000-2000 mghrs 3 30% 500-1000 mghrs 2 11% 2000-3000 mghrs 20 cm 3 25% 1000-2000 mghrs 4 25% 1000-1500 mghrs 2 7% 3000-4000 mghrs 25 cm 3 20% 2000-3000 mghrs 4 20% 1000-2000 mghrs 30 cm and 3 4 10% 10% 3000-4000 mghrs 2000-3000 mghrs more 5 10% 1000-2000 mghrs For bladder, rectum, and prostate the number of fields is about the same. In these cases Roentgen ray and radium treatment can also be combined according to the method discussed above. A further field of application of homogeneous irradia- tion, according to Juengling and others, is the treatment of tuberculosis of the joints and lungs. The dosage pre- sents no difficulties since only small doses need be applied. Homogeneous irradiation of the joints can be accom- plished according to Juengling by building a pasteboard box around the region to be treated and filling the box with bolus alba. Also, if water bags are superposed, the EXAMPLES OF TREATMENTS 265 raying can be carried out from three or four sides with- out the danger of the overlapping of beams. An approxi- mately homogeneous irradiation can be carried out with thin patients by means of one anterior and one posterior field; with thick patients 4 fields can be given obliquely. (c) A third physical class of areas to be rayed is char- acterized by regions of intermediate depth. On the one hand, the depth of the area is too large to permit of treat- ment by means of a single field and, on the other hand, the position of the area is not central, as in the preceding cases (uterus, prostate, stomach, liver, hypophysis, etc.), so that the region is not well adapted to the cross fire method. The treatment of these cases therefore involves difficulties. The following methods have been developed and used in these cases: (1) The irradiation can be carried out with one field and very penetrating radiation, heavily filtered Roent- gen rays and a focus skin distance up to 1 meter being used. Besides, a slight overdosage is applied to the sur- face, so that in spite of the absorption in the surface layers a sufficient intensity reaches the interior. This method has been tried by Seitz and Wintz on carcinomata of the vulva; with a focus distance of 1 meter a strong erythema dose is applied to the surface of the vulva; the dosage must be carried out very carefully since overexposure would result in an extremely painful and difficultly healing inflammation. Cancer nodules in the breasts, as well as the axillary glands in cases of breast carcinomata, have been treated by the same method. The results were not very satisfactory. The method has been abandoned therefore or combined with others. The sin- gle field is still retained in those cases where the desired dose is of such a magnitude that it may be applied with- 266 PRINCIPLES OF X RAY AND RADIUM DOSAGE out resorting to large focus distances and overexposure. These conditions are fulfilled when the spleen or the thymus gland are to be given a stimulating dose since only Vio to Ys of a unit skin dose is required. The single field is also applicable to deep seated cancroids in the skin, since in these cases large doses at the surface are appropriate; Perthes applies a dose strong enough to cause vesication; Juengling applies up to 150% of a unit skin dose with slightly filtered rays (1-3 mm aluminum), and up to 130% of a unit skin dose with a mm zinc filter. The treatment of carcinomata of the tongue from the surface by means of gamma rays and with a strong over- exposure of the surface also belongs under this head. (2) The second method consists in artificially placing the affected region at a depth at which cross fire irradia- tion can be carried out from several sides. This method is always advisable when a homogeneous irradiation is desirable or at least is not injurious. These conditions are fulfilled in carcinomata of the vulva. The region of the vulva can easily be rayed homo- geneously when the patient is rayed in a distended recum- bent position with the legs close together. An anterior, a posterior, and possibly two lateral fields are applied. The adjustment is made so that the central ray strikes a little above the vulva. In order to avoid an overexpos- ure due to the addition of direct and scattered radiation in the region of the nates, a paraffine wedge is inserted which absorbs the direct radiation. The conditions are the same in the irradiation of the axilla. If the arm is placed close to the body, a homogen- eous irradiation can be obtained by means of two fields one anteriorly, one posteriorly. In special cases a third EXAMPLES OF TREATMENTS 267 field can be added. According to Dessauer a field given through the arm is suitable; however, in the author’s opinion a field applied through the shoulder is more appropriate, since it is directed toward axillary glands and moreover also strikes the supraclavicular glands. Dessauer has proposed to ray carcinomata of the breast homogeneously as a whole (breast, axillary, infra and supraclavicular glands) by means of large fields. A large anterior field extends over the breast and infraclavicular glands; a smaller field is applied from the rear toward the axilla, while a field from above strikes the supraclavicular glands and the axilla. The addition of these fields pro- duces a high intensity in the interior. A decrease of intensity from the surface to the interior of the breast can only be avoided if a large dorsal field is applied, how- ever, by this means the lungs are easily overexposed; it is particularly dangerous to give the same treatment to both the right and left half of the body since burns in the lungs may result. In this case only small dorsal fields should be applied locally toward the axilla. Figure 66 shows a cross section through the thorax somewhat below the axilla and slightly above the breast. Two fields each with an intensity of 100% at the surface are given. The isodosage lines show the intensity dis- tribution. Toward the interior the intensity is fairly homogeneous but falls off from right to left. Due to this fact the tissue of the lungs is somewhat protected. If this method of treatment does not apply sufficient energy to the axillary glands, a radium tube can be intro- duced into the axilla. If the beta rays are totally absorbed and the tube is placed two centimeters from the surface of the skin, a certain depth action can be produced, which adds to the Roentgen radiation. 268 PRINCIPLES OF X RAY AND RADIUM DOSAGE Also in the radiation treatment of carcinomata of the larynx we are dealing with the irradiation of a region which lies only a short distance beneath the surface. On account of the limited permissible range of the dose, which is from 90 to 100% of a unit skin dose, Holfelder states that a homogeneous irradiation is appropriate. Moreover, there is little danger of injuring neighboring organs. Breast Carcinoma, 2 Ports of Entry, Thorax. 200 KV. 24 MM Cu. 50 CM F. S. D. Homogeneous irradiation in this case presents some difficulty because there is danger of overlapping of the beams. Hence in this case the use of water bags is advis- able, at least for the two oblique fields. A third field can EXAMPLES OF TREATMENTS 269 be applied from the rear. On account of the small diam- eter of the region rayed only about half of an erythema dose can be applied to each surface. Figure 67 shows a treatment case in which a homo- geneous irradiation of the region of the larynx is ■^XAJ-O- OutX^Ji Fi(k.(s>J, Cancer of Larynx. Treatment with Superposed Layers. 200 KV. 24 MM Cu. 50 CM F. S. D. 270 PRINCIPLES OF X RAY AND RADIUM DOSAGE attained. A superficial layer of 1 cm of water is used and three fields at each of which 50% of a unit skin dose is applied. A uniform application of from 90 to 100% is not difficult by this method. (3) Since the two methods just described are not always adequate for producing sufficient intensity at a small depth, due to the fact that either the overlying tis- sue or the surrounding tissue receives too strong a dose, attempts have been made to produce a local action by imbedding the source of radiation in the interior of the affected region. For this purpose radium needles are placed in the tumor at easily calculated distances apart and allowed to remain until an application of 100 mghrs has been made, or emanation tubes are placed in the tumor by means of an obtuberator and allowed to remain there since they slowly lose their activity. The number of ampules and the number of millicurie-hours can be deduced from preceding considerations. This method is best suited to tumors which are located at a small depth; hence it is applicable to carcinomata of the breast and metastases of the same, as well as to carcinomata of the tongue, lips, and cheeks, as soon as these penetrate to deeper layers. In a much larger number of cases than are now so treated, radium needles or emanation tubes should be inserted at the time of operation, when an exploratory operation discloses the futility of surgical intervention. The method can also be used for treating tumors at a greater depth if they can be made accessible. This is often possible in cases of sarcomata as well as car- cinomata of the prostate and of the stomach. The injection of radioactive solutions cannot be used for the local treatment of tumors since the radioactive substances are rapidly distributed over the whole body EXAMPLES OF TREATMENTS 271 and are partially deposited in the blood forming- organs. (d) A fourth group are those cases which require a general treatment of the whole body. Of course, a general treatment can be carried out only with small doses. Large doses, such as those neces- sary in the treatment of carcinomata, would be fatal if applied to the whole body. On the other hand, small doses, which stimulate metabolism, lower the blood pres- sure, and accelerate secretion, can easily be tolerated by the body. The general treatment, therefore, finds its chief application in internal medicine in the treatment of such conditions, as gout, arthritis, myalgia, anaemia, leukemia, Hodgkins disease, constipation, etc. The treatment can be carried out by any method which sends a small stimulating energy through the whole body. Best suited is the administering of radio- active substances internally; this can be done by: Intravenous injection, Drinking or swallowing of radioactive water or pills, Inhaling of emanation. The irradiation of the whole body with hard Roentgen radiation should also produce similar effects; however, so far no systematic experiments have been conducted along this line. The general treatment of the whole body with large doses would seem appropriate in cases of general carcino- matosis, as well as sarcoma of the lymphatic system, or sarcoma metastases. However, since the body could not endure such an irradiation, the treatment can only be carried out in parts by dividing the body up into a number of sections and treating these separately. For example, in cases of general carcinomatosis, first the involved skin areas can be treated with soft rays, then the deep seated 272 PRINCIPLES OF X RAY AND RADIUM DOSAGE carcinomata by cross fire methods, and, finally, the swol- len lymphatic glands can be subjected to strong radiation. Of course, a cure is not possible but the disease can be held in check for some time by this method. (e) Many cases of Roentgen or radium treatment present must greater difficulties than those discussed in the preceding examples. In these cases a combination of the methods described is desirable. The best known example of this class is the combination of intensive local treatment with homogeneous irradiation of the adjacent regions. In this category belongs the most commonly used and already described method of uterus treatment, in which the primary carcinoma is attacked by intense radium irradiation while the Roentgen irradiation serves to reduce recurrent growths or to prevent their formation. The treatment of carcinoma of the rectum should be car- ried out in a similar manner; besides a strong irradiation of the seat of the cancer, a homogeneous irradiation of the inguinal glands ought to be carried out. Under this head also belongs the combination treatment of epithe- liomata of the tongue, of the lips, and of the cheeks, that is to say the localized treatment of the growth proper with very intense doses in conjunction with the homo- geneous irradiation of the involved lymphatic tissues with small doses. The treatment of sarcoma is very simi- lar; in addition to the local treatment of the tumor proper, the surrounding region should be safeguarded against swelling and metastases by appropriate treatment. Finally, all methods which tend to increase the power of resistance of the patient and to improve the general health of the patient must be combined with radiation treatment—however, this subject is beyond the scope of this book. EXAMPLES OF TREATMENTS 273 § 3. Case record blank. A case record blank is appended, which gives a very comprehensive view of the treatment sequence and fur- thermore serves as a record. Patient Age Disease, etc Application Distribution Reac- Constants Date Area, cm2 MA min Mg hrs Area X ray Radi- um Total tion (200) KV (Jan.) (2)... (Ant. 202) . . (400) (100) (—) (100) (Nor- mal Erythe- (5) MA ($4) mm Cu ... (3)... (Post. 202).. (375) Tumor.. .. (90) (00) (00) Tumor (5)... (Rt. 10x15). (450) Bowels.. .. (90) (40) (130) Blad- der ir- ritated) (50) cm FSD.. (7)... (9)... (Lft. 10x10). (Uterus).. .. (450) (1500) Broad Lig- aments. Axillary (86) (15) (101) (—) glands... (1.5)mm(brass) (0) cm Distance (Mar.) (5) Intrave- nously.. .. Intrave- 2ccm (9) (5 Micro- nously.... Intrave- 2ccm (12) gram per ccm nously.... 2ccm Radium (16) Intrave- Solution) .. nously 2ccm In the first column all the treatment factors are noted, both for the Roentgen and the radium treatments. In addition, the concentration of radium emanation in the treatment rooms, the quantity of radium solution given intravenously* etc., is noted. This brief notation of the constant factors saves much space. Blank forms can be printed with the smybols MA, K.V., etc., on the card. In the illustration the entries which may be printed directly on the form have been given in heavy type; the values to be entered in ordinary type. 274 PRINCIPLES OF X RAY AND RADIUM DOSAGE The second column gives the date of the treatment. In the third column are noted the regions of applica- tion and size of field. In this, as well as in the next col- umn, nothing can be printed in advance since the entries vary from case to case. In the fourth column is entered the amount of energy applied to the separate areas; MA min., in the case of Roentgen rays; mghrs. in the case of radium; solutions are given in terms of cubic centimeters; inhalation of emanation in hours, etc. The fifth column is reserved for the estimated or measured distribution of the applied energy. The dose given to the skin as well as to organs which are to be protected (bladder, rectum, spleen, etc.), in particular the dose administered to the area to be treated (tumor, glands, etc.) are entered here. A few designations can be printed on the form, but it is better to enter the organs involved from case to case. The Roentgen and radium energies are entered separately, and their sum is also noted. At the present stage of the technique it is best to state the energy in percentage of the skin dose, the latter being designated by 100%; the quantity can also be stated in physical units, in e or F units, but by this method the comparison of Roentgen and radium energies becomes more difficult. In the last column the reaction of the organ treated and the reaction of the patient as a whole is noted. The entire arrangement gives a comprehensive view of the chosen technique, the applied physical dose and the particular and general reactions produced; in this way it records that which is essential from the viewpoint of practical treatment and scientific experimentation.