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This report presents the background and some preliminary findings during 1961 in a large-scale study of medical x-ray procedures in the offices of private physicians in New York City. RADIATION DOSE FROM DIAGNOSTIC MEDICAL X-RAY PROCEDURES TO THE POPULATION OF NEW YORK CITY M. B. Heller, M.S.; H. Bl-ztz, E.E.; B. Pasternack, Ph.D.; and M. Eisenbud, Sc.D. THE benefits to mankind from med- lation than all other sources combined. ical x-ray diagnostic procedures in (It does, without question, constitute the past few decades have been sub- most of the total radiation received by stantial and the practice of modern those individuals who are exposed.) medicine is highly dependent on their It is quite clear that a large source use. However, there are potential haz- of the variation in dose estimates among ards associated with these procedures countries cited in the United Nations due to the biological effects of ionizing Report is a result of marked differences radiation. In recent years, increased in- in diagnostic x-ray technic. Most of the terest in the magnitude of the popula- references pertaining to dose estimates tion's exposure to x-ray has developed in the 1958 UN document were based as part of the greater attention being on research performed in large, modern shown to all sources of exposure to ioniz- hospitals or clinics in the respective ing radiation, both artificial and natural. countries. For many of the examinations, The principal sources of ionizing ra- dosimetric data for only a limited num- diation to which the population is ex- ber of patients are presented. This num- posed are the natural radioactive back- ber of examinations may be sufficient ground, occupational exposure, and the for a valid representation in one hos- clinical uses of x-rays and isotopes. The pital or one clinic, but certainly con- reports of the Federal Radiation Coun- stitutes an inadequate representation of cil' and the 1958 report of the United an entire community whether city, state, Nations Scientific Committee on the Ef- or nation. Similarly, the recent esti- fects of Atomic Radiation,2 the most mates of gonadal dose included in the authoritative compendia on the subject, 1962 UNSCEAR Report3 are again de- present the estimates of these compo- rived from data obtained from studies nents shown in Table 1. This table in- relating to large hospitals and medical dicates two conditions which are sub- centers mostly located in countries where stantiated by reading most of the re- medical care programs are either na- maining literature on the subject: (1) tionalized or strongly controlled. Esti- There is more uncertainty regarding med- mates derived from such data cannot be ical radiation dose than any other com- considered to constitute a reliable as- ponent of population exposure, and (2) sessment of the patient dose in nations diagnostic exposure may account for where large proportions of medical diag- more human radiation dose to the popu- nostic x-ray examinations are performed SEPTEMBER. 19964 1 551 Table 1-Components of Population Radiation Exposure Annual Dose (mrem) Mean Source Gonad Dosel Marrow Dose2 External Cosmic rays 32- 73 28 Terrestrial radiation 25- 75 47 Atmospheric radiation 2 2 Internal K-40 19 11 C-14 1.6 1.6 Rn-Tn 2 2 Ra - 0.5 Total 80-171 92 Genetically Per capita Significant Mean Dose Marrow Dose Medical (exposure to patients) Diagnostic 40-240 Ranges beyond 100 Therapy 12 No estimate Occupational <2 1-3 in private physicians' offices. Aside from presenting dose estimates directly re- this type of apparent biased estimation, lated to the study by applying a set of a large source of the variation among laboratory or field data which was meas- these nations can be ascribed, broadly, to ured in an unrelated institution or area. differences in diagnostic x-ray technic Gonadal doses were then calculated in among different institutions, specialties, many cases without modification of the and individuals. laboratory data with respect to physical Variation resulting from differences and anthropometric factors except, per- in diagnostic x-ray technic may be sub- haps, for age and sex classification. divided as follows: "(a) patient factors, Clearly, there exists a need to study the (b) procedural factors, (c) equipment sources of variation which influence the factors, and (d) professional factors."4 estimates of population radiation dose Within these groups there are numerous derived from medical x-ray procedures. additional contributing factors such as This report presents the background and anthropometric relationships (including some of the preliminary findings during thickness of part), field location, field 1961 from our study of medical x-ray size, peak kilovolts (KVP), filtration, procedures in private physicians' offices and individual variations in the per- in New York City. The primary guide formance of fluoroscopic examinations. to the early objectives of the present Previous field studies relating to pa- study was the ICRP/ICRU report en- tient dose have been reported in this titled "Exposure of Man to Ionizing country.5'6 They generally present data Radiation Arising from Medical Proce- on examination frequency, but fail in dures."7 1552 VOL. 54, NO. 9. A.J.P.H. MEDICAL X-RAY PROCEDURES Objectives sociated with the physician's x-ray prac- The principal objectives and scope of tice, viz.: type and manufacturer of unit, the entire study may be summarized as added filtration, dark adaptation time follows: for fluoroscopy, use of gonadal shields, field size of radiographic cones, output A. Collect, assemble, and furnish information and half-value layer (HVL) at standard on the kind, operational state, and number of diagnostic and therapeutic x-ray units in settings, and so forth. New York City. The technical data for radiography B. Estimate the frequency of various medical and fluoroscopy, which are recorded on procedures which involve diagnostic and the P-2 form, include: KVP, milli- therapeutic radiation exposure to residents ampere-seconds (MaS), field size, name of New York City according to equipment used, technic, specialty of physician, age of examination and anatomical empha- and sex of patients, and seasonal variation. sis, projection, target to film distance, C. Estimate per capita gonadal and bone mar- film speed and size, and use of grids row radiation dose to the population of New and screens. Information on the patient York City. D. Determine the feasibility of using informa- includes: age, sex, height, weight, race, tion obtained in objectives A, B, and C borough of residence, and the thickness above in epidemiological studies. Identify of part being examined. population exposure groups worthy of future study of possible delayed radiation effects. Data Collection Method Design and Methods After careful consideration of all the The performance of the work entailed methods proposed by the ICRP and UN in the present study has been divided Task Committees, the direct sampling of into three phases. These, in sequence, private physicians' offices was chosen. are: (1) diagnostic private x-ray in- The method selected permits measure- stallations, (2) diagnostic institutional ments of physical machine variables by x-ray installations, and (3) therapeutic trained personnel and allows the estab- installations. The remainder of this re- lishment of rapport between our field port will concern itself primarily with workers and the physicians' office staff. the data collected during the early part This rapport has contributed greatly to of the survey of private medical offices. the accurate reporting of data; particu- It is to be understood that the private larly when the personnel performing patients exposed to units in these offices routine radiography in private physi- represent the population from which our cians' offices are frequently not inti- sample data has been assembled. Hos- mately familiar with the technical vari- pital outpatients, inpatients, and those ables associated with x-ray technic. exposed in clinics are considered in a The forms used were designed in such future phase of this study. a way as to permit the recording of all pertinent data in the simplest possible Required Data way. The function of the P-1 form is the collection of all information which is The data collected for each patient ap- either constant or requires only one pearing in this study are considered to measurement. This is completed by the be sufficient for the computation of dose field worker during the initial interview. by any of several methods. The tech- The P-2 forms are designed for the re- nical data are recorded by use of the cording of examinations and variables two forms designated as P-1 and P-2. related to individual examinations and The P-1 form is used in the initial inter- patients. A further feature of the P-2 view to record general characteristics as- form is that several examinations or ex- SEPTEMBER, 1964 1 553 Table 2-Main Study Sample No. Installations Installation Total No. of Total No. of To Be Sampling Specialty Installations* X-ray Units* Sampled Fraction GP 2,401 3,696 302 0.1299 Chest diseases 220 351 114 0.518 Dermatology 17 23 11 0.649 ENT 47 59 28 0.595 Gyn. and obst. 56 80 28 0.50 Internal med. 1,098 1,879 222 0.202 Neurology 4 6 4 1.0 Occupational med. 99 208 50 0.505 Ophthalmology 4 5 4 1.0 Orthopedics 121 168 61 0.504 Pediatrics 205 261 104 0.507 Radiology 205 569 103 0.501 Surgery 211 336 106 0.501 Urology 134 170 67 0.50 Gastroent. 7 14 7 1.0 Hematology 2 2 2 1.0 Allergy 9 9 9 1.0 Physical med. 2 4 2 1.0 Endocrinology 2 2 2 1.0 Mobile chest x-ray 3 9 3 1.0 Total 4,847 7,851 1,229 0.2535 * As of March 15, 1961. posures may be recorded on the same to all sample units during a stated pe- page for one patient, but only one pa- riod of time. With regard to the se- tient may be recorded per page. lected sample, patients who are under X-ray output, half-value layer, and the care of physicians other than the field alignment are being obtained at in- physician with whom the studied unit stallations with an Electronic Instru- is associated are included, and patients ments Limited ionization chamber and under the care of the physician being electrometer of the type used in the studied who are referred elsewhere for British study of medical exposure.8 diagnostic x-ray procedures are ex- cluded. Each installation is normally The Sample Unit sampled for a period of four calendar weeks. The sample unit, for the purpose of Names and addresses of patients are this study, is defined as the x-ray equip- not sought since the purpose of this ment which belongs to or is registered study is the characterization of dose in the name of a physician maintaining associated with specific diagnostic pro- an office in New York City. All such cedures and an indication of exposure installations comprise the universe from groups according to type of examnination which the sample is selected. Con- for possible future epidemiological study ceptually, the exposed population of in- rather than the identification of specific dividuals consists of all patients exposed heavily exposed individuals. Hence, it is 1554 VOL. 54, NO. 9. A.J.P.H. MEDICAL X-RAY PROCEDURES Table 3-Sample Number of Patients and ing criteria: (1) expected contribution Exposures, 1961 to gonadal dose per examination per- Radiography No. of No. of formed, (2) expected patient workload, Procedure Patients Exposures (3) expected variability in technic, (4) number of installations in the specialty, Radiography only 7,167 19,276 and (5) size of installations within the Radiography and specialty. Those specialties with less fluoroscopy 1,089 4,920 than ten installations are being sampled 8,256 24,196 entirely. All others except general prac- tice, internal medicine, and dermatology are being sampled at 50 per cent. Gen- Fluoroscopy No. of No. of eral practice and internal medicine rep- Procedure Patients Sessions resent the largest number of installations Fluoroscopy only 1,281 1,645 and are therefore being sampled at only Radiography and 12 and 20 per cent respectively. Derma- fluoroscopy 1,089 1,096 tologists have an intermediate sampling fraction due to their expected low diag- 2,370 2,741 nostic x-ray workload. Deviations from the proposed sampling fractions result from the distribution of specialty instal- emphasized that the identity of physi- lation types within the boroughs. cians and their patients is never released from the study office and is known only Organization of Field Work by those personnel working directly on the field and office staffs for the purpose The boroughs were subdivided into of communicating with the physician. Area Work Zones (AWZ). Those AWZ's Data are always presented in grouped with a large number of installations form within a given specialty. were then further subdivided. The order of sampling the AWZ's was then selected Sample Selection randomly. Each month the names of the physicians in the Area Work Zones The medical offices which are being to be sampled are sent by our field super- studied were chosen from the registry of visor to the appropriate county med- x-ray machines in New York City main- ical societies. The executive secretaries, tained by the Office of Radiation Con- in turn, inform the physicians and urge trol in the New York City Health De- their cooperation by means of a letter. partment. The total registration of diag- Our field interviewers then call the nostic medical installations arranged by physicians for initial interview appoint- specialty and number of units through ments. The initial interview consists of March, 1961, is shown in Table 2. This providing detailed information to the table also contains sampling fractions physician and his staff on the objectives and numbers of installations being and motivations of this study, the col- sampled. It is of interest to note that lection of information for completion of while 7.2 per cent of the x-ray units in the P-1 form, and instructing a mem- private offices are owned by radiologists, ber of the physician's staff on the com- 71 per cent are in the hands of gen- pletion of P-2 forms. Half-value layer, eral practitioners and internists! A 25 output and beam alignment are meas- per cent random sample, stratified by ured subsequently by our physicist. specialty and borough, was chosen after The field interviewer makes a weekly weighting each specialty by the follow- follow-up visit at which time the P-2 SEPTEMBER, 1964 1 555 CHEST EXAMINATIONS VA 22.7 EXPOSURES: Fm CO L-iJ 4000 3000 TOTAL = 19,276 CHEST= 4,464 % EXPOSURES: < 30 YRS 20.4 < 40 YRS 37.4 12.8 17.0 H 20.0 19.7 Of) 2000- 0 x 57 1000- 7 24.8 22.0 7 22.6 21.3 1.9 25.3 7/ / / /7 0- 112.9_- '730.0 0.9 10-19 20-29 30-39 40-49 50-59 >59 AGE GROUP Figure 1-Age Distribution. Chest Examinations as a Percentage of Total Exposures forms are checked for completeness. The computed. The general procedure con- recorder is informed of proper proce- sists of first computing the field size dure, if necessary, and the forms are of the x-ray beam at the patient from brought back from the field for editing the cone data and target to film distance. and transcription to code sheets for key The type of examination and anthropo- punching. Preliminary pilot study field metric information will then be used to work was begun in February, 1961, and determine the area and location of the the main study field work commenced beam projected on the patient. Given in July, 1961. this information, it will be determined if the gonads are in the direct beam. Data Processing Since the output and HVL for each ma- chine are measured at a standard KVP The study group has designed several (with the amount of filtration normally IBM cards to control and process the used in place) the output and HVL at information pertinent to the study and any other KVP can be computed from utilizes the following IBM equipment for its routine work: keypunch, verifier, sorter, and tabulator. More voluminous and complex computations, such as long- Table 4-Age Distribution of Persons Exposed Radiographically term statistical analyses and dose cal- culations, are being programed for the UN Report This Study university's computer facilities. Age % % Dose Computation 0-14 15 3.7 15-29 20 16.8 The gonadal dose to each patient ob- 30-49 35 37.1 served in the study will be individually >49 30 42.4 1556 VOL. 54. NO. 9. A.J.P.H. MEDICAL X-RAY PROCEDURES Table 5-Examination Distribution that year, 80 per cent of the 418 phy- sicians contacted* cooperated with the Mean No. study. The number of patients and ex- Per cent of Expo- of Total sures per posures are presented in Table 3. Radiography Examinations Examination The age distribution in ten-year in- tervals, for all exposures, is shown in Chest 37 1.28 Figure 1. Chest film exposures are in- Lumbosacral dicated as a percentage of the exposures spine 4.1 2.47 in each age interval. The over-all per- Upper GI 4.6 7.50 Knee 3.7 4.01 centage of chest examinations is 37 per cent. The percentage of total exam- Fluoroscopy inations under ages 30 and 40 are of Chest 65 interest, since it is estimated that 50 Upper GI 17 per cent of all children are born to par- Barium enema 11 ents under 30 years of age and 90 per cent are born to parents under 40 years of age. The age distribution data in- dicate an apparently lower percentage standard data. The air dose at the pa- of examinations in the 0-14 year age tient's skin is computed as a function group than that estimated by Laughlin4 of KVP and target to skin distance. The in the UN/ICRP task report as shown gonadal dose is then determined by di- in Table 4. From this table it is seen rect computation or by modification for that the UN/ICRP estimates agree with technical and anthropometric factors our findings in the two middle ranges and interpolation of a standard set of and that the difference in the number laboratory phantom data such as that of exposures in the less than 15-year-age developed at the Sloan-Kettering Insti- group is made up in the greater than tute.9 Bone marrow dose may be com- 49-year group. puted in a similar manner. The most frequent examinations are given in Table 5. The mean number of Analysis exposures for all radiographic examina- tions was found to be 2.37. The most The data presented here are derived * Excluding 95 who were unable to partici- from the analysis of information col- pate because of death or sale of equipment lected during the year 1961. During and/or practice. Table 6-Chest Radiography Mean Field Size Mean Mean Mean Specialty (cm) MaS KVP TFD (in.) GP 96.15 17.3 70.5 70.2 Chest 87.46 16.0 70.3 69.7 Internal medicine 83.10 17.0 74.7 70.5 Radiology 74.78 21.1 71.3 69.6 Occupational medicine* 62.58 28.0 78.0 65.9 All spec.t 77.1 17.6 71.8 71.1 * Photoroentgen examinations included. t Excluding occupational medicine. SEPTEMBER. 1964 I 557 Table 7-Per cent of Total Chest Films Table 8 pertains to the field sizes associated with radiographic chest exam- Specialty inations. The relative size of field may, Projection GP % Chest % Radiology perhaps, be better appreciated in remem- bering that for the 14 by 17 inch film A.P. 17.3 5.3 5.3 the diagonal dimension is 22 inches or P.A. 68.8 86.5 67.8 Lat. 3.7 7.0 26.0 56 centimeters. If the x-ray tube is aligned with the film cassette, this is the diameter of beam required to completely cover the film. It is seen that among frequent type of examination involved the installations within a given medical the chest. Table 6 summarizes the im- specialty, there is relatively little varia- portant technical variables in chest tion in field size. The magnitude of radiography for several specialties. The field sizes, associated with various spe- mean MaS for all specialties is 17.6. Our cialties, are presented more clearly in analyses show that this variable, which Figure 2. The effects on dose of the is proportional to dose, would be re- large number of anterior-posterior pro- duced by 15 per cent if appropriate in- jections coupled with the field size used tensifying screens were used for all by general practitioners can be clearly examinations. The 28 MaS figure, the appreciated. high KVP and low target to film dis- tance for occupational medicine, reflect Comments the extensive use of photofluorographic equipment in that specialty. The high It is hoped that the information to be MaS value for radiology is due to the gained from the present study will lead relatively larger proportion of lateral to a more realistic estimation of popula- projections performed in that specialty tion radiation exposure from medical as indicated in Table 7. The higher x-rays than has heretofore been avail- percentage of anterior-posterior projec- able in the United States. Our data, tions by general practitioners will tend through the end of 1961, indicate that to increase the gonadal dose contributed many of the accepted estimatesI1012 (on by this examination, since in females which population dose estimates have the iliac bones are not interposed be- been based) may be low by as much tween the target and the ovaries and in as one or two orders of magnitude. These males the muscles which would be inter- estimates are misleading because they posed in the posterior-anterior projec- are based on the use of optimum tech- tion are not interposed. nic and therefore indicate what the dose Table 8-Summary of Field Size Analysis for Chest Radiography Mean Standard Coefficient Number of Field Size Error of Mean of Variation Specialty Examinations (cm) (cm) of Mean (%) GP 274 96.15 8.00 8.33 Chest 649 87.46 5.88 6.72 Internal med. 893 83.10 9.77 11.76 Radiology 512 74.78 2.59 3.46 Occupational med. 1,849 62.58 5.13 8.12 I 558 VOL. 54, NO. 9. A.J.P.H. MEDICAL X-RAY PROCEDURES INT. MED. 33.0" G.P. 38.0" to the gonadal dose from chest examina- CFHEST 34.5" tions-the most frequent radiographic procedure and the one expected to be most standardized. ) REFERENCES 1. Background Material for the Development of Radia. tion Protection Standards. Report No. 1. Washing- ton, D. C.: Federal Radiation Council (May), 1960. 2. Report of the United Nations Scientific Committee RADIOL. 29.5 OCC I MED. 24.6"1 on the Effects of Atomic Radiation. 13th Session Suppl. No. 17 (A/3838), New York, 1958. 3. . 17th Session Suppl. No. 16 (A/5216), New York, 1962. 4. "Recommendations for Plan of Study of Task I Through V Within the United States," under UNSCEAR, ICRP. In Hearings, 85th Session, United States Congressional Joint Committee on Atomic Energy, Special Subcommittee on Radiation, on the Nature of Radiation Fallout and Its Effect on Man, Part 1 (June), 1957, pp. 859-888. 5. Brown, R. F.; Heslep, J.; and Eads, W. Radiology HEIGHT 5' 8" 14" x 17" FILIM 74:353 (Mar.), 1960. 6. Billings, M. S.; Norman, A.; and Greenfield, M. A. Figure 2-Field Sizes for ChesiIt Examia- Ibid. 69:37-51 (July), 1957. tion 7. "Exposure of Man to Ionizing Radiation Arising from Medical Procedures." ICRP/ICRU Phys. in Med. and Biol. 2:108, 1957. 8. Radiological Hazards to Patients. Second Report of the Committee to the Ministry of Health, Depart- should be rather than what tlhe dose is. ment of Health for Scotland, London, 1960. Epp, E. R.; Weiss, H.; and Laughlin, J. S. Brit. The true dose to the populati on is tem- m J. Radiol. 34:85100 (Feb.), 1961. pered by technics which exiiibit great 10. Webster, E. W., and Merrill, 0. E. New England J. Med. 257:811, 1957. variability. Our data, thus far, have 11. Ardran, G. M., and Crooks, H. E. Brit. J. Radiol. demonstrated the large variiability of 30:295, 1957. 12. Wolfson, J. L., and Garrett, C. National Research some technical factors relatinig directly I Council of Canada, No. 5377, 1959. The authors are associated with the Environmental Radiation Laboratory of the Institute of Environmental Medicine, New York University Medical Center, New York, N. Y. This study was performed under U. S. Public Health Service Contract No. SAph 73722. This report is a revision of a paper read at the annual meeting of the Health Physics Society, June 11-14, 1962, in Chicago, Ill. SEPTEMBER. 1964 155S9
"RADIATION DOSE FROM DIAGNOSTIC MEDICAL RAY"