- Email: [email protected]
Radiation Exposure of Patient and Personnel During Urographic Procedures
THE JOURNAL OF UROLOGY
Vol. 81, No. 1, January 1959 Printed in U.S.A..
RADIATION EXPOSURE OF PATIENT AND PERSONNEL DURING UROGRAPHIC PROCEDURES H. S. WEENS, R. H. ROHRER, PH.D. AND H. D. YOUMANS, JR., A.B. From the Department of Radiology, Emory University School of Medicine, Emory University, Ga. INTRODUCTION
In view of recent re-evaluation of genetic and somatic effects of radiation exposures, the problems of radiation hazards in diagnostic radiology should be of particular concern to the urologist. X-ray examinations of the abdomen and pelvis may account for more than 50 per cent of all medical gonadal radiation exposure.1 From 10 to 20 per cent of all diagnostic radiation exposure to ovaries and testes stems from urographic examinations.2 It is likely that the amount of somatic radiation exposure received by patients undergoing various types of urographic procedures may be found in a similar range. RADIATION DOSIMETRY
In order to understand radiation exposure to patients and personnel, a limited knowledge of radiation dosimetry is necessary. Three units are often used. These are the roentgen (r), the rad, and the rem. The roentgen (r), the basic unit of radiation exposure, is expressed in terms of the ionizing effect of radiation on 1 cc air. Its definition is such that it is easy to measure with accuracy. However, biological systems respond to the amount of energy they actually absorb rather than the amount of radiation to which they are exposed. The rad is a unit of dose absorbed from a radiation beam by one gram of material. Direct measurement of this quantity is not always possible, but it has more meaning in terms of the effect of radiation on such materials as tissues, bones, or fluids; and it may be computed by the use of conversion tables if the exposure in roentgens is known. The rem is a measurement of the biological effectiveSupported by U. S. Public Health Service . Grant No. C-3109. Read at annual meeting of Southeastern Section of American Urological Association, Inc., Hollywood, Fla., January 12-16, 1958. . 1 Stanford, R. W. and Vance, J_.: Quantity of radiation received by reproductive organs_ of patients during ro'!ltine diagnostic x-ray examma. tions. Brit. J. Radiol., 28: 266--273, 1955. 2 Martin, J. H.: Radiation 4oses to_ gont1;ds m diagnostic radiology and their relat10nship to long-term genetic hazard. M. J. Austral., 2: 806-810, 1955. 232
ness of absorbed doses due to various forms of radiation such as x-rays, alpha particles, or neutrons. It is related to the rad by the simple expression Dose in rems = Dose in rads X RBE where RBE is the relative biological effectiveness of the form of radiation used. (This factor is unity for x-rays.) For the practicing urologist it may suffice to know that in the range of diagnostic radiology the r, the rad, and the rem are almost equivalent and interchangeable as far as the soft tissues of the human body are concerned. The calibration of instruments available for measuring radiation doses has been standardized so that with the exercise of proper care in their operation, reliable dosage levels may be determined. One should be aware that in the particular case of measuring radiation doses in short diagnostic x-ray exposures, technical limitations of the dosimeters may be exceeded. 3 If this is not recognized, errors in data may result which may explain to some extent the variations of the results in published reports. Most information pertaining to radiation exposure in diagnostic radiology has been obtained by experiments in phantoms made of "tissue-equivalent" materials in shapes which are presumed to represent the true conditions encountered in the human body. Recent improvements in instruments have made possible an increasing number of observations based on measuring radiation exposure on the surface or in body cavities of patients, and the results of these observations are now becoming available. RADIATION EFFECTS ON THE HUMAN BODY
Radiation effects on the human body may be genetic or somatic in character. Much of the information concerning these effects lacks scientific precision and many assumptions have to be made in order to fill wide 3 Laughlin, J. S., Meurk, M. L., Pullman, I. a~d Sherman, R. S.: Bone, skin, and gonadal doses m routine diagnostic procedures. Am. J. Roentgen.,
78: 961-982, 1957.
233
RADIATION EXPOSURE DURING UROGRAPHY
gaps of present knowledge. Thus animal data have to be applied to man. Large radiation dosages have to be extrapolated to lower dosage levels prevailing in the field of diagnostic radiology. As far as human radiation exposure goes, admittedly inaccurate estimations have to be accepted. Nevertheless, to those concerned with radiation protection and the design and maintenance of safety measures, estimations of this type are of appreciable importance. GENETIC RADIA'l'ION EFFECTS
It is well established that irradiation of the reproductive cells induces mutation of the genetic material which may be transmitted to future generations. These genetic rndiation effects are accumulative so that small amounts of radiation received over a prolonged period of time are completely additive. Radiation induced mutations arc similar in every respect to spontaneouslv occurring mutations and have to be regarded ;s harmful and undesirable. i\.ccording to best presently av:ciilablc evidence 3, radiation exposure of 40-80 roentgens to the germ cells may double the spontaneous mutation ratc. 4 There is no precise information available as to the amount of gonadal radiation received by our population as the result of various types of medical x-ray exposure. On the basis of some estimates it has been suggested that with presently prevailing medical and dental radiation levels a 10 per cent increase of the spontaneous mutation rate would eventually occur. 4 The annual birth rate in the United States is above 4,000,000. Each year approximately 80,000 infants are born with tangible physical and mental defects attributable to harmful mutations. A 10 per cent increase of the mutation rate due to medical radiation exposure woulcl thus eventually result in an annual increase of 8,000 defective infants after ten to forty generations. 4 Over the first generation (30 years) probably 800 defective infants would be born annually. At first glance such figures appear alarming. They have to be considered however in proper balance to the ten times much larger number of spontaneously occurring mutations and the decreased morbidity and mortality rates of the entire population as the result of diagnostic x-ray procedures. 4 Glass, B.: The genetic basis for the limitation of radiation exposure. Am . .J. Roentgen .. 78: 955-
960, 1957.
.
SOMA'l'IC RADIATION EFFECTS
Somatic radiation effects manifest themst\lves in injury to the body or organ systems of the irradiated individual. In the exposure range pertaining to diagnostic radiology, such radiation effects as shortening of lifespan and induction of leukemia have received foremost consideration. More recently, increasing attention has been to the effects of radiation on the fetus in utero, which may be more radiation sensitive certain early phases of gestation. 5 , 5 It would be beyond the scope of this paper to describe somatic radiation effects in detail but the problems of lifespan shortening and radiation-induced lrnkemia shall be considered. Shortening of Zifespan. In animal shortening of lifespan has been well documented. as a result of chronic irradiation exposure.' However, with very small doses of radiation, ,mch as 0.5 r per day or less, shortening of th1c has not been demonstrated so far. 8 The number of· animals utilized in these studies was small and the normal life expectancy of these animals wns short in comparison to human lifespan. [n recent report of human radiation exposure it could be observed that the mean age of death of radiologists who are exposed to small increments of radiation was 60.5 years compared with fib.7 for other physicians. 9 Lewis10 analyzed these data and demonstrated that with proper consideration of age distribution in these statistics no difference in life expectancy could be detected. In a careful analysis of published animal observations Failla and McClement8 postulated that for chronic radiation exposure at a level of 0.5 r per day or less, one roentgen of accumulated dose (total exposure) would shorten the human lifespan fo,· one day. Leukemia. The increased incidence of leukemia 5 Russell, L. B. and Russell, W. L.: hazards to the embryo and fetus. u,ecuu"'"
369-376, 1952. 6
Stewart, A., Webb, J., Giles. D. and Hewit.L
p.: l\~alfgn3:nt disease in childhood and diagnostic.
1rradrnt10n m utero. Lancet, 2: 447, 1956. 7 Lorenz, E.: Some biologic effects of long continued irradiation. Am. ,J. Roentgen., 63: 176-185 1950.
'
Failla, G. and McClement, P.: The shortening of life by chronic whole-body irradiation . Am . .I. Roentgen., 78: 946-954, 1957. 9 vVarren, S.: Longevity and causes of death from irradiation in physicians. J.A.lVLA. 162: 8
464-468, 1956.
'
Lewis, E. B.: Leukemia and ionizing ra.dia~ tion. Science, 125: 965-972, 1957. 10
234
H. S. WEENS, R. H. ROHRER AND H. D. YOUMANS, JR.
among radiologists has been emphasized in several well documented reports. In the 15 year period from 1938 to 1952, 17 deaths from leukemia occurred among the radiologists of the United States, five times as many as expected among nonradiologist physicians.10 Unfortunately there is little accurate information available concerning the amount of radiation received by these individuals who were occupationally subject to chronic radiation exposure at a time when standards of radiation protection were inadequate according to present concepts. That leukemia may be induced by ionizing radiation is well established by animal experiments.7 Most recently Lewis10 in a comprehensive analysis of human radiation exposure (radiologists, patients receiving therapeutic irradiation, atom bomb survivors) has attempted a quantitative appraisal of this radiation risk for given amounts of accumulated radiation. According to his calculations the annual chance of developing leukemia per rad of accumulated dose is two in one million for total body exposure and smaller for partial body exposure. In other words, the annual risk of developing leukemia for an individual who has absorbed a total body dose of five rad would be ten in one million. For partial body exposure it would be correspondingly smaller. The spontaneous incidence of leukemia is approximately 60 to 70 in one million per year with annual deaths of approximately 10,000 to 12,000 in the United States. One has to keep in mind that studies of this type are at the very best .estimates and not fully proved by observations in the range of diagnostic x-ray procedures. MAXIMUM PERMISSIBLE DOSE
Any evaluation of the dangerous side effects of x-ray requires the following considerations. Man throughout his evolution has been subjected to so-called natural radiation. This radiation stems from external sources (cosmic rays, gamma rays of environment) as well as internal sources (naturally occurring isotopes absorbed by air, food and drink). It has been determined that the human body receives in this manner a dose of three to four rad per generation (30 years). 11 This varies somewhat with location, altitude, and environment such as housing. Evidently this amount of radiation has proved to be a tolerable 11 Spiers, F. W.: Radioactivity in man and his environment. Brit. J. Radial., 29: 409-417, 1956.
one over generations and may serve to some extent as a yardstick in assessing additional radiation exposure. It would appear reasonable that any additional radiation exposure of similar magnitude would not prove to be too dangerous. The potentially harmful effects of x-rays have to be compared with the benefits which diagnostic radiology has brought about in modern medicine. The annual number of deaths from tuberculosis in the United States has decreased from over 80,000 in 1930 to about 17,000 in 1954.12 There is little doubt that diagnostic x-ray procedures have been in a large measure responsible for effective tuberculosis control. There are annually many thousands of human lives saved by the early detection and treatment of gastrointestinal, urinary tract, and pulmonary malignancy. There have been tremendous contributions of diagnostic radiology to the early recognition and treatment of other illnesses. One should keep in mind that in the presence of medical x-ray exposure, the average length of life in the United States has increased more than ten years from 1925 to 1955.13 Diagnostic x-ray examinations do not involve total body exposure but are usually confined to moderate or small segments of the human body. This limitation of the radiation field will reduce somatic radiation hazards proportionately in comparison with so-called total body exposure. Such observations should not invite complacency. Because there are no threshold levels for certain radiation injuries, efforts have to be made to keep radiation exposure to personnel and patient at a minimum but at the same time adequate for the continuation of high standards of diagnostic accuracy. As the dangerous side effects of ionizing radiation became increasingly apparent, various interested groups concerned themselves with the design of protective methods and the establishment of dosage levels which could be regarded as reasonably safe. Out of these efforts the concept of maximum permissible dosage gradually evolved. It is noteworthy that this maximum permissible dose has been reduced several times during the last two decades. Initially, the recommended exposure levels were largely designed for those 12 Anderson, R. J.: Tuberculosis morbidity and mortality. Facts and trends. Public Health Reports, 71: 194-200, 1956. 13 Vital Statistics, special report, 46: 260-270,
1957.
RADL\TION EXPOSURE DURING UIWGRAPHY
........
As
---1h'--t---f___,____,,________,--v'
~ 1 I
I
I
I
EXPOSURE 80 l
=
FACTORS !OOmos
80 KVP,
3.1 mm. AL
Without
Added
Cone
14
4
2
0
FEET
100 mos
HVL= 3.1 mm. AL
Added F1ltrot1on 2.5mm. Al
4
3
2
0
~
Filtration 2,5 mm. AL
17 inch
Field Srze
FEET
Fm. l. Radiation levels sunounding typical urographic installation. A, values without X·ra.y· cone. B, vn)ues with x-ray cone limiting x-ray beam to 14 X 17 inch field size. Exposure factors apply to one three x-ray expos mes according to technique and size of patient (Ir = 1000 mr). occupationally exposed to repeated small amounts of radiation. l\fore recently, however, as a.n ever increasing segment of our population is being exposed to medical and nonmedic2l radiation, recommendations concerning gonadal radiation exposure of all individuals have been made. According to latest recommend:1tions14 the maximum permissible accumulative dose for the occup:1tiona.lly exposed is given at 5 · (N-18) rems where N is the age of the: individual. This applies to all essential organs except the skin for which this value rna.y be double, medical rndiation exposure in thr'.se individuals is not considered to have ha.rmfnl effects on radiation tolerance:. In practice in the field of diagnostic radiology this is equivalent to a radiation exposure of 0.1 r per wc:ek. For limited periods of time: the weekly exposure: may attain 0.3 r per week but the: annual exposme rate shall remain at a level of 5.0 r per year. For the ,, hole population a permissible gonadal radiation exposure has been established for all sources of ra.dia.tion, medical as wc:11 as nonmedical and background radiation. This is given as 14,000,000 rems for 1,000,000 of population from conception to the age of 30, and one-third that amount in ea.ch decade thereafter. From 14 J\Ia.ximurn permissible radiation exposure to man. A preliminary statement of the National Committee on radiation protection and mea.surement. Radiology, 68: 260-261, 1957.
these figures it is clearly implied that an av1:ra.ge dose is conceived and that there will be instances in which by necessity medical radiation exposure: will have to exceed the indicated levels. IUDIATION EXPOSURE OF PERSONNEL ANH PATIENTS
Personnel exposure. Radiation levels to whicb urologist may be exposed vnry with the type of equipment employed, the x-rny technique utilized, and the working lmbits of the individual surgeon. Radiation levels surrotrnding a. urograpbic installa.tion as determined pliautom experiments a.re presented in figure ] l, A shows the radiation levels in milliroc:ntgens pc:r 100 millia.mpc:re-seconds (equivalent to one tu three x-rny expoRures) ,Yithout the use of mi x-my beam limiting device. Figure I, B shows radiation levels of the same x-ray equipment but with the x-ra.y beam sharply defined to Lhe field size (14 by 17 inches). It is clearly evident that x my beam limita tion will appreciably redL1ce radiation 1evelR i.n proximity to the urographic table. N everthe less, c:ven if such a bea.m limiting device JR used, radiation levels remain rdativdy For this reason the dose received by a working in proximity to the urogrnphic fable could readily exceed accepted ma.ximum permissible doses (0.1 r per week) with a rela.ti vdy small number of urogra.phic procedures ..-\s the urologist may object to the installation of a firm
236
H. S. WEENS, R. H. ROHRER AND H. D. YOUNIANS, JR.
1. Radiation exposure dose (mr). Single roentgenogram. Kidneys, ureters lilnd bladder
TABLE
Skin Testes I OvarKVPt MASt Jes ------ --
Authors
Ritter, Warren & 1300 Pendergrass 15 Weens, Clements & Tolan 16 Martin 2 Stanford & Vance 1 Hol & Koren 17 Ardran & Crooks 18
480
150
62
100
50 74-88 20-40 140 250 69 200 40 220 15 90 0.5* 95
72 72 120 75
100 100 13
80
* Shielded with lead rubber
t Kilovolt-peak
t Milliampere-seconds TABLE
2. U rethrocystography. Radiation exposure to testes (mr). Single roentgenogram
Authors
With I !WithShl:,ld Shield KVP* MASt
800 550 110 Weens, Rohrer 375 & Youmans
Mag;nusson 19 Hol &Koren17
2-14
51 24
64 72 120 80 80
Radiation Shield
Special brass capsule
100 13 30 30
I Lead foil (0.24 mm.) I Lead foil (0.36 mm.)
* Kilovolt-peak
firm protective shield at the head end of the table appears desirable. Patient exposure. A number of studies have been carried out in patients and phantoms with reference to radiation exposure pertaining to urographic procedures. Data collected from the literature and obtained in our own laboratory are presented in tables 1 and 2. It should be noted that there are discrepancies in these observations. These differences may be attributed to large variations in x-ray technique, apparatus, and size of patients and phantoms. To a large extent these differences may also be caused by the type of measuring instruments available at the time of these investigations. As previously stated, dosimeters have certain technical limitations with reference to short diagnostic x-ray exposures. It is conceivable that in the future more uniform information will be obtained. Nevertheless, the range of radiation exposure is well reflected in the data contained in these tables. PROTECTIVE MEASURES
Table 1 indicates that radiation levels to patients may be relatively high if a large series of examinations is performed. One should keep in mind that this would occur only in a rather small
t Milliampere-seconds protective shield which might interfere with his working conditions he should prot.cct himself under these circumstances with a light lead apron (,),-::i: mm. of lead equivalent). Such aprons can be made very flexible and should eliminate more than 80 per cent of the scattered radiation. As many urographic procedures are carried out under anesthesia, the anesthesiologist may be subjected to scattered radiation. If the anesthesiologist has to remain close to the urographic table during x-ray exposures, installation of a 15 Ritter, V. W., Warren, S. R. and Pendergrass, E. P.: Roentgen doses during diagnostic procedures. Radiology, 59: 238-250, 1952. 16 Weens, H. S., Clements, J. L. and Tolan, J. H.: Radiation dosage to female genital tract during fluoroscopic procedures. Radiology, 62: 745-749, 1954. 17 Hol, R. and Koren, K.: Protection measures in roentgen diagnostics with reference to doses inducing mutations. Acta Radiol., 44: 471-478, 1955. 18 Ardran, G. M. and Crooks, H. E.: Gonad radiation dose from diagnostic procedures. Brit. J. Radiol., 30: 295-297, 1957. 19 Magnusson, W.: A device for the protection of the testicle in roentgen examinations of adjacent organs and bones. Acta Radiol., 37: 288-290, 1952.
Fm. 2. Urethrography. Three layers of thin lead foil (total lead thickness 0.36 mm.) surrounding gonads will eliminate more than 90 per cent of testicular radiation exposure.
RADIATIOX EXPOSURE DURIXG UROGRAPHY
287
:B'rn. 3. High speed intensifying screens and high speed films permit reduction of radiation exposure to approximately one-third. Roentgenogram taken with high speed film and high speed screen an air dose of 150 mr, whereas 450 mr are necessary to obtain simifar result with conventional screen material segment of our population, frequently in the older age groups. Fortunately we are able today-with surprisingly simple steps and procedures-to effect a very significant reduction of radiation exposure to patient and personneL These measures shall be briefly discussed. 1) Elimination of unsatisfactory examinations. Adequate equipment is a prerequisite for roentgen examinations. In addition, many rocntgenograms prove to be unsatisfactory due to faulty position, motion, improper exposure and darkroom technique. Attention to these problems would eliminate many unnecessary repeat examinations. 2) Field limitation. Urographic x-ray tables are often not equipped with proper field limitation devices. Round x-ray cones provide a radiation field much larger than necessary. Cones, fixed or variable lead diaphragms should be rectangular for most purposes and tho field of radiation should never exceed the area of clinical interest. Field limitation is of particular importance in pediatric radiology where radiation fields of excessive dimensions are often employed. Though shielding of the ovaries is presently not feasible in abdominal x-ray examinations, the testicular dosage may be considerably reduced by
confining the lower edge of the x-ray beam to the symphysis pubis. This may be simply accomplished by placing a lead rubber shield over the genital area up to the pubic rami. llnder tht sc circumstances testicular radiation exposure stems largely from the patient's body and could not be further reduced without placing a radiation shield between the gonads and the perincum. 20 In the case of urethrocystography radintion to the gonads is relatively high unless special pro. tective measures are employed (table 2). Though certain protective devices have been designed,"' the shielding of the gonads with thin lead foil (0.3 mm. lead equivalent) may prove to be a most simple procedure effecting reduction of radiation dose to a small percentage of the primary beam. (fig. 2). 3) Filtration. Adding a filter of 3 mm. of aluminum to the x-ray beam will eliminate of the soft x-radiation to the superficial tissues and skin. Since these soft x-rays contribute little to the image formation, they ma.y therefore he eliminated from the field of raclia,tion. 4) Film development. There is a. tendency in many offices and hospitals to overexpose and 0
20
Youmans, H. D., Rohrer, R. IL a,nd ·weens,
H. S.: Unpublished observations.
238
H. S. WEENS, R. H. ROHRER AND H. D. YOUMANS, ,JR.
underdevelop x-ray films. If roentgenograms are developed for five minutes at 68°, radiation exposure may be significantly reduced. 5) Film and screen selection. Recent advances in the development of high speed films and high speed screens make it now possible to reduce radiation exposure to less than one-half of previous exposure doses. If such factors as proper selection of film and screen material, proper film development and limitation of x-ray beam size are combined, radiation exposure may be reduced to about onethird or less without sacrificing the number of essential x-ray examinations. Such improvements would be of no avail unless they receive the full support of all physicians and personnel participating in radiologic examinations (fig. 3). SUMMARY AND CONCLUSIONS
During recent years an increasing amount of information concerning various biologic radiation
effects has become available. Though much of this information is still incomplete and not precise, it has permitted some preliminary estimation of the magnitude of several types of radiation hazards. As there are for certain radiation injuries no threshold levels, medical x-ray examinations have to be performed with the minimum exposure dose necessary for adequate diagnosis. Advances in x-ray screen and film materials as well as technical improvements allow considerable diminution of medical radiation exposure. Such reduction of x-ray exposure cannot be effected, however, without the diligent efforts and full support of all physicians and personnel participating in radiologic procedures. Radiation hazards have to be considered in their proper perspective. On the basis of presently available evidence the benefits of properly selected and conducted x-ray examinations for our whole population far outweigh their harmful side effects.
Vol. 81, No. 1, January 1959 Printed in U.S.A..
RADIATION EXPOSURE OF PATIENT AND PERSONNEL DURING UROGRAPHIC PROCEDURES H. S. WEENS, R. H. ROHRER, PH.D. AND H. D. YOUMANS, JR., A.B. From the Department of Radiology, Emory University School of Medicine, Emory University, Ga. INTRODUCTION
In view of recent re-evaluation of genetic and somatic effects of radiation exposures, the problems of radiation hazards in diagnostic radiology should be of particular concern to the urologist. X-ray examinations of the abdomen and pelvis may account for more than 50 per cent of all medical gonadal radiation exposure.1 From 10 to 20 per cent of all diagnostic radiation exposure to ovaries and testes stems from urographic examinations.2 It is likely that the amount of somatic radiation exposure received by patients undergoing various types of urographic procedures may be found in a similar range. RADIATION DOSIMETRY
In order to understand radiation exposure to patients and personnel, a limited knowledge of radiation dosimetry is necessary. Three units are often used. These are the roentgen (r), the rad, and the rem. The roentgen (r), the basic unit of radiation exposure, is expressed in terms of the ionizing effect of radiation on 1 cc air. Its definition is such that it is easy to measure with accuracy. However, biological systems respond to the amount of energy they actually absorb rather than the amount of radiation to which they are exposed. The rad is a unit of dose absorbed from a radiation beam by one gram of material. Direct measurement of this quantity is not always possible, but it has more meaning in terms of the effect of radiation on such materials as tissues, bones, or fluids; and it may be computed by the use of conversion tables if the exposure in roentgens is known. The rem is a measurement of the biological effectiveSupported by U. S. Public Health Service . Grant No. C-3109. Read at annual meeting of Southeastern Section of American Urological Association, Inc., Hollywood, Fla., January 12-16, 1958. . 1 Stanford, R. W. and Vance, J_.: Quantity of radiation received by reproductive organs_ of patients during ro'!ltine diagnostic x-ray examma. tions. Brit. J. Radiol., 28: 266--273, 1955. 2 Martin, J. H.: Radiation 4oses to_ gont1;ds m diagnostic radiology and their relat10nship to long-term genetic hazard. M. J. Austral., 2: 806-810, 1955. 232
ness of absorbed doses due to various forms of radiation such as x-rays, alpha particles, or neutrons. It is related to the rad by the simple expression Dose in rems = Dose in rads X RBE where RBE is the relative biological effectiveness of the form of radiation used. (This factor is unity for x-rays.) For the practicing urologist it may suffice to know that in the range of diagnostic radiology the r, the rad, and the rem are almost equivalent and interchangeable as far as the soft tissues of the human body are concerned. The calibration of instruments available for measuring radiation doses has been standardized so that with the exercise of proper care in their operation, reliable dosage levels may be determined. One should be aware that in the particular case of measuring radiation doses in short diagnostic x-ray exposures, technical limitations of the dosimeters may be exceeded. 3 If this is not recognized, errors in data may result which may explain to some extent the variations of the results in published reports. Most information pertaining to radiation exposure in diagnostic radiology has been obtained by experiments in phantoms made of "tissue-equivalent" materials in shapes which are presumed to represent the true conditions encountered in the human body. Recent improvements in instruments have made possible an increasing number of observations based on measuring radiation exposure on the surface or in body cavities of patients, and the results of these observations are now becoming available. RADIATION EFFECTS ON THE HUMAN BODY
Radiation effects on the human body may be genetic or somatic in character. Much of the information concerning these effects lacks scientific precision and many assumptions have to be made in order to fill wide 3 Laughlin, J. S., Meurk, M. L., Pullman, I. a~d Sherman, R. S.: Bone, skin, and gonadal doses m routine diagnostic procedures. Am. J. Roentgen.,
78: 961-982, 1957.
233
RADIATION EXPOSURE DURING UROGRAPHY
gaps of present knowledge. Thus animal data have to be applied to man. Large radiation dosages have to be extrapolated to lower dosage levels prevailing in the field of diagnostic radiology. As far as human radiation exposure goes, admittedly inaccurate estimations have to be accepted. Nevertheless, to those concerned with radiation protection and the design and maintenance of safety measures, estimations of this type are of appreciable importance. GENETIC RADIA'l'ION EFFECTS
It is well established that irradiation of the reproductive cells induces mutation of the genetic material which may be transmitted to future generations. These genetic rndiation effects are accumulative so that small amounts of radiation received over a prolonged period of time are completely additive. Radiation induced mutations arc similar in every respect to spontaneouslv occurring mutations and have to be regarded ;s harmful and undesirable. i\.ccording to best presently av:ciilablc evidence 3, radiation exposure of 40-80 roentgens to the germ cells may double the spontaneous mutation ratc. 4 There is no precise information available as to the amount of gonadal radiation received by our population as the result of various types of medical x-ray exposure. On the basis of some estimates it has been suggested that with presently prevailing medical and dental radiation levels a 10 per cent increase of the spontaneous mutation rate would eventually occur. 4 The annual birth rate in the United States is above 4,000,000. Each year approximately 80,000 infants are born with tangible physical and mental defects attributable to harmful mutations. A 10 per cent increase of the mutation rate due to medical radiation exposure woulcl thus eventually result in an annual increase of 8,000 defective infants after ten to forty generations. 4 Over the first generation (30 years) probably 800 defective infants would be born annually. At first glance such figures appear alarming. They have to be considered however in proper balance to the ten times much larger number of spontaneously occurring mutations and the decreased morbidity and mortality rates of the entire population as the result of diagnostic x-ray procedures. 4 Glass, B.: The genetic basis for the limitation of radiation exposure. Am . .J. Roentgen .. 78: 955-
960, 1957.
.
SOMA'l'IC RADIATION EFFECTS
Somatic radiation effects manifest themst\lves in injury to the body or organ systems of the irradiated individual. In the exposure range pertaining to diagnostic radiology, such radiation effects as shortening of lifespan and induction of leukemia have received foremost consideration. More recently, increasing attention has been to the effects of radiation on the fetus in utero, which may be more radiation sensitive certain early phases of gestation. 5 , 5 It would be beyond the scope of this paper to describe somatic radiation effects in detail but the problems of lifespan shortening and radiation-induced lrnkemia shall be considered. Shortening of Zifespan. In animal shortening of lifespan has been well documented. as a result of chronic irradiation exposure.' However, with very small doses of radiation, ,mch as 0.5 r per day or less, shortening of th1c has not been demonstrated so far. 8 The number of· animals utilized in these studies was small and the normal life expectancy of these animals wns short in comparison to human lifespan. [n recent report of human radiation exposure it could be observed that the mean age of death of radiologists who are exposed to small increments of radiation was 60.5 years compared with fib.7 for other physicians. 9 Lewis10 analyzed these data and demonstrated that with proper consideration of age distribution in these statistics no difference in life expectancy could be detected. In a careful analysis of published animal observations Failla and McClement8 postulated that for chronic radiation exposure at a level of 0.5 r per day or less, one roentgen of accumulated dose (total exposure) would shorten the human lifespan fo,· one day. Leukemia. The increased incidence of leukemia 5 Russell, L. B. and Russell, W. L.: hazards to the embryo and fetus. u,ecuu"'"
369-376, 1952. 6
Stewart, A., Webb, J., Giles. D. and Hewit.L
p.: l\~alfgn3:nt disease in childhood and diagnostic.
1rradrnt10n m utero. Lancet, 2: 447, 1956. 7 Lorenz, E.: Some biologic effects of long continued irradiation. Am. ,J. Roentgen., 63: 176-185 1950.
'
Failla, G. and McClement, P.: The shortening of life by chronic whole-body irradiation . Am . .I. Roentgen., 78: 946-954, 1957. 9 vVarren, S.: Longevity and causes of death from irradiation in physicians. J.A.lVLA. 162: 8
464-468, 1956.
'
Lewis, E. B.: Leukemia and ionizing ra.dia~ tion. Science, 125: 965-972, 1957. 10
234
H. S. WEENS, R. H. ROHRER AND H. D. YOUMANS, JR.
among radiologists has been emphasized in several well documented reports. In the 15 year period from 1938 to 1952, 17 deaths from leukemia occurred among the radiologists of the United States, five times as many as expected among nonradiologist physicians.10 Unfortunately there is little accurate information available concerning the amount of radiation received by these individuals who were occupationally subject to chronic radiation exposure at a time when standards of radiation protection were inadequate according to present concepts. That leukemia may be induced by ionizing radiation is well established by animal experiments.7 Most recently Lewis10 in a comprehensive analysis of human radiation exposure (radiologists, patients receiving therapeutic irradiation, atom bomb survivors) has attempted a quantitative appraisal of this radiation risk for given amounts of accumulated radiation. According to his calculations the annual chance of developing leukemia per rad of accumulated dose is two in one million for total body exposure and smaller for partial body exposure. In other words, the annual risk of developing leukemia for an individual who has absorbed a total body dose of five rad would be ten in one million. For partial body exposure it would be correspondingly smaller. The spontaneous incidence of leukemia is approximately 60 to 70 in one million per year with annual deaths of approximately 10,000 to 12,000 in the United States. One has to keep in mind that studies of this type are at the very best .estimates and not fully proved by observations in the range of diagnostic x-ray procedures. MAXIMUM PERMISSIBLE DOSE
Any evaluation of the dangerous side effects of x-ray requires the following considerations. Man throughout his evolution has been subjected to so-called natural radiation. This radiation stems from external sources (cosmic rays, gamma rays of environment) as well as internal sources (naturally occurring isotopes absorbed by air, food and drink). It has been determined that the human body receives in this manner a dose of three to four rad per generation (30 years). 11 This varies somewhat with location, altitude, and environment such as housing. Evidently this amount of radiation has proved to be a tolerable 11 Spiers, F. W.: Radioactivity in man and his environment. Brit. J. Radial., 29: 409-417, 1956.
one over generations and may serve to some extent as a yardstick in assessing additional radiation exposure. It would appear reasonable that any additional radiation exposure of similar magnitude would not prove to be too dangerous. The potentially harmful effects of x-rays have to be compared with the benefits which diagnostic radiology has brought about in modern medicine. The annual number of deaths from tuberculosis in the United States has decreased from over 80,000 in 1930 to about 17,000 in 1954.12 There is little doubt that diagnostic x-ray procedures have been in a large measure responsible for effective tuberculosis control. There are annually many thousands of human lives saved by the early detection and treatment of gastrointestinal, urinary tract, and pulmonary malignancy. There have been tremendous contributions of diagnostic radiology to the early recognition and treatment of other illnesses. One should keep in mind that in the presence of medical x-ray exposure, the average length of life in the United States has increased more than ten years from 1925 to 1955.13 Diagnostic x-ray examinations do not involve total body exposure but are usually confined to moderate or small segments of the human body. This limitation of the radiation field will reduce somatic radiation hazards proportionately in comparison with so-called total body exposure. Such observations should not invite complacency. Because there are no threshold levels for certain radiation injuries, efforts have to be made to keep radiation exposure to personnel and patient at a minimum but at the same time adequate for the continuation of high standards of diagnostic accuracy. As the dangerous side effects of ionizing radiation became increasingly apparent, various interested groups concerned themselves with the design of protective methods and the establishment of dosage levels which could be regarded as reasonably safe. Out of these efforts the concept of maximum permissible dosage gradually evolved. It is noteworthy that this maximum permissible dose has been reduced several times during the last two decades. Initially, the recommended exposure levels were largely designed for those 12 Anderson, R. J.: Tuberculosis morbidity and mortality. Facts and trends. Public Health Reports, 71: 194-200, 1956. 13 Vital Statistics, special report, 46: 260-270,
1957.
RADL\TION EXPOSURE DURING UIWGRAPHY
........
As
---1h'--t---f___,____,,________,--v'
~ 1 I
I
I
I
EXPOSURE 80 l
=
FACTORS !OOmos
80 KVP,
3.1 mm. AL
Without
Added
Cone
14
4
2
0
FEET
100 mos
HVL= 3.1 mm. AL
Added F1ltrot1on 2.5mm. Al
4
3
2
0
~
Filtration 2,5 mm. AL
17 inch
Field Srze
FEET
Fm. l. Radiation levels sunounding typical urographic installation. A, values without X·ra.y· cone. B, vn)ues with x-ray cone limiting x-ray beam to 14 X 17 inch field size. Exposure factors apply to one three x-ray expos mes according to technique and size of patient (Ir = 1000 mr). occupationally exposed to repeated small amounts of radiation. l\fore recently, however, as a.n ever increasing segment of our population is being exposed to medical and nonmedic2l radiation, recommendations concerning gonadal radiation exposure of all individuals have been made. According to latest recommend:1tions14 the maximum permissible accumulative dose for the occup:1tiona.lly exposed is given at 5 · (N-18) rems where N is the age of the: individual. This applies to all essential organs except the skin for which this value rna.y be double, medical rndiation exposure in thr'.se individuals is not considered to have ha.rmfnl effects on radiation tolerance:. In practice in the field of diagnostic radiology this is equivalent to a radiation exposure of 0.1 r per wc:ek. For limited periods of time: the weekly exposure: may attain 0.3 r per week but the: annual exposme rate shall remain at a level of 5.0 r per year. For the ,, hole population a permissible gonadal radiation exposure has been established for all sources of ra.dia.tion, medical as wc:11 as nonmedical and background radiation. This is given as 14,000,000 rems for 1,000,000 of population from conception to the age of 30, and one-third that amount in ea.ch decade thereafter. From 14 J\Ia.ximurn permissible radiation exposure to man. A preliminary statement of the National Committee on radiation protection and mea.surement. Radiology, 68: 260-261, 1957.
these figures it is clearly implied that an av1:ra.ge dose is conceived and that there will be instances in which by necessity medical radiation exposure: will have to exceed the indicated levels. IUDIATION EXPOSURE OF PERSONNEL ANH PATIENTS
Personnel exposure. Radiation levels to whicb urologist may be exposed vnry with the type of equipment employed, the x-rny technique utilized, and the working lmbits of the individual surgeon. Radiation levels surrotrnding a. urograpbic installa.tion as determined pliautom experiments a.re presented in figure ] l, A shows the radiation levels in milliroc:ntgens pc:r 100 millia.mpc:re-seconds (equivalent to one tu three x-rny expoRures) ,Yithout the use of mi x-my beam limiting device. Figure I, B shows radiation levels of the same x-ray equipment but with the x-ra.y beam sharply defined to Lhe field size (14 by 17 inches). It is clearly evident that x my beam limita tion will appreciably redL1ce radiation 1evelR i.n proximity to the urographic table. N everthe less, c:ven if such a bea.m limiting device JR used, radiation levels remain rdativdy For this reason the dose received by a working in proximity to the urogrnphic fable could readily exceed accepted ma.ximum permissible doses (0.1 r per week) with a rela.ti vdy small number of urogra.phic procedures ..-\s the urologist may object to the installation of a firm
236
H. S. WEENS, R. H. ROHRER AND H. D. YOUNIANS, JR.
1. Radiation exposure dose (mr). Single roentgenogram. Kidneys, ureters lilnd bladder
TABLE
Skin Testes I OvarKVPt MASt Jes ------ --
Authors
Ritter, Warren & 1300 Pendergrass 15 Weens, Clements & Tolan 16 Martin 2 Stanford & Vance 1 Hol & Koren 17 Ardran & Crooks 18
480
150
62
100
50 74-88 20-40 140 250 69 200 40 220 15 90 0.5* 95
72 72 120 75
100 100 13
80
* Shielded with lead rubber
t Kilovolt-peak
t Milliampere-seconds TABLE
2. U rethrocystography. Radiation exposure to testes (mr). Single roentgenogram
Authors
With I !WithShl:,ld Shield KVP* MASt
800 550 110 Weens, Rohrer 375 & Youmans
Mag;nusson 19 Hol &Koren17
2-14
51 24
64 72 120 80 80
Radiation Shield
Special brass capsule
100 13 30 30
I Lead foil (0.24 mm.) I Lead foil (0.36 mm.)
* Kilovolt-peak
firm protective shield at the head end of the table appears desirable. Patient exposure. A number of studies have been carried out in patients and phantoms with reference to radiation exposure pertaining to urographic procedures. Data collected from the literature and obtained in our own laboratory are presented in tables 1 and 2. It should be noted that there are discrepancies in these observations. These differences may be attributed to large variations in x-ray technique, apparatus, and size of patients and phantoms. To a large extent these differences may also be caused by the type of measuring instruments available at the time of these investigations. As previously stated, dosimeters have certain technical limitations with reference to short diagnostic x-ray exposures. It is conceivable that in the future more uniform information will be obtained. Nevertheless, the range of radiation exposure is well reflected in the data contained in these tables. PROTECTIVE MEASURES
Table 1 indicates that radiation levels to patients may be relatively high if a large series of examinations is performed. One should keep in mind that this would occur only in a rather small
t Milliampere-seconds protective shield which might interfere with his working conditions he should prot.cct himself under these circumstances with a light lead apron (,),-::i: mm. of lead equivalent). Such aprons can be made very flexible and should eliminate more than 80 per cent of the scattered radiation. As many urographic procedures are carried out under anesthesia, the anesthesiologist may be subjected to scattered radiation. If the anesthesiologist has to remain close to the urographic table during x-ray exposures, installation of a 15 Ritter, V. W., Warren, S. R. and Pendergrass, E. P.: Roentgen doses during diagnostic procedures. Radiology, 59: 238-250, 1952. 16 Weens, H. S., Clements, J. L. and Tolan, J. H.: Radiation dosage to female genital tract during fluoroscopic procedures. Radiology, 62: 745-749, 1954. 17 Hol, R. and Koren, K.: Protection measures in roentgen diagnostics with reference to doses inducing mutations. Acta Radiol., 44: 471-478, 1955. 18 Ardran, G. M. and Crooks, H. E.: Gonad radiation dose from diagnostic procedures. Brit. J. Radiol., 30: 295-297, 1957. 19 Magnusson, W.: A device for the protection of the testicle in roentgen examinations of adjacent organs and bones. Acta Radiol., 37: 288-290, 1952.
Fm. 2. Urethrography. Three layers of thin lead foil (total lead thickness 0.36 mm.) surrounding gonads will eliminate more than 90 per cent of testicular radiation exposure.
RADIATIOX EXPOSURE DURIXG UROGRAPHY
287
:B'rn. 3. High speed intensifying screens and high speed films permit reduction of radiation exposure to approximately one-third. Roentgenogram taken with high speed film and high speed screen an air dose of 150 mr, whereas 450 mr are necessary to obtain simifar result with conventional screen material segment of our population, frequently in the older age groups. Fortunately we are able today-with surprisingly simple steps and procedures-to effect a very significant reduction of radiation exposure to patient and personneL These measures shall be briefly discussed. 1) Elimination of unsatisfactory examinations. Adequate equipment is a prerequisite for roentgen examinations. In addition, many rocntgenograms prove to be unsatisfactory due to faulty position, motion, improper exposure and darkroom technique. Attention to these problems would eliminate many unnecessary repeat examinations. 2) Field limitation. Urographic x-ray tables are often not equipped with proper field limitation devices. Round x-ray cones provide a radiation field much larger than necessary. Cones, fixed or variable lead diaphragms should be rectangular for most purposes and tho field of radiation should never exceed the area of clinical interest. Field limitation is of particular importance in pediatric radiology where radiation fields of excessive dimensions are often employed. Though shielding of the ovaries is presently not feasible in abdominal x-ray examinations, the testicular dosage may be considerably reduced by
confining the lower edge of the x-ray beam to the symphysis pubis. This may be simply accomplished by placing a lead rubber shield over the genital area up to the pubic rami. llnder tht sc circumstances testicular radiation exposure stems largely from the patient's body and could not be further reduced without placing a radiation shield between the gonads and the perincum. 20 In the case of urethrocystography radintion to the gonads is relatively high unless special pro. tective measures are employed (table 2). Though certain protective devices have been designed,"' the shielding of the gonads with thin lead foil (0.3 mm. lead equivalent) may prove to be a most simple procedure effecting reduction of radiation dose to a small percentage of the primary beam. (fig. 2). 3) Filtration. Adding a filter of 3 mm. of aluminum to the x-ray beam will eliminate of the soft x-radiation to the superficial tissues and skin. Since these soft x-rays contribute little to the image formation, they ma.y therefore he eliminated from the field of raclia,tion. 4) Film development. There is a. tendency in many offices and hospitals to overexpose and 0
20
Youmans, H. D., Rohrer, R. IL a,nd ·weens,
H. S.: Unpublished observations.
238
H. S. WEENS, R. H. ROHRER AND H. D. YOUMANS, ,JR.
underdevelop x-ray films. If roentgenograms are developed for five minutes at 68°, radiation exposure may be significantly reduced. 5) Film and screen selection. Recent advances in the development of high speed films and high speed screens make it now possible to reduce radiation exposure to less than one-half of previous exposure doses. If such factors as proper selection of film and screen material, proper film development and limitation of x-ray beam size are combined, radiation exposure may be reduced to about onethird or less without sacrificing the number of essential x-ray examinations. Such improvements would be of no avail unless they receive the full support of all physicians and personnel participating in radiologic examinations (fig. 3). SUMMARY AND CONCLUSIONS
During recent years an increasing amount of information concerning various biologic radiation
effects has become available. Though much of this information is still incomplete and not precise, it has permitted some preliminary estimation of the magnitude of several types of radiation hazards. As there are for certain radiation injuries no threshold levels, medical x-ray examinations have to be performed with the minimum exposure dose necessary for adequate diagnosis. Advances in x-ray screen and film materials as well as technical improvements allow considerable diminution of medical radiation exposure. Such reduction of x-ray exposure cannot be effected, however, without the diligent efforts and full support of all physicians and personnel participating in radiologic procedures. Radiation hazards have to be considered in their proper perspective. On the basis of presently available evidence the benefits of properly selected and conducted x-ray examinations for our whole population far outweigh their harmful side effects.