Methods of Estimating the Medical Exposure to Ionizing Radiation

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Contributors To This Report leader, from.material furnished by the following: National Leader Task I11 Leadercountry Czechoslovakia Jan fliiller Norway Kristian Koren

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This study is directed primarily to a review of sampling procedures which could be applied in a survey to detenrnine the average gonad dose received by patients from exposure to medical sources of ionizing radiation. volve the selection at random of' a repres&tative sample of: medical institutions in which most of the exposure is given. tive sample may be studied by letter qyestionnaire or personal contact, and instruments may be furnished as an adjunct of the survey. The three sampling methods discussed in- (1) individuals in the medical men who are responsible f o r administering the exposure; and (3) In each case the represents; B e method recommended for the primary survey is personal contact of the (surveyorwith the medical institution either w i t h or without the furnishing of instruments. pilot scale before lrndertaking the primary survey in order to permit a better selection of the sample and to make certain that all the data needed in .the final returns are collected w i t h the required accuracy in the most economical way possible. should be given to a system that has sufficient flexibility to permit its extension in order to accumulate information on the rehtionship between dose from ionizing radiation and somatic damage, as well as genetic m e . Several types of presurveys should be conducted on a

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This report of Task I11 is limited t o a cursory review of various sampling procedures that might be applied i n estimating the medical exposure t o ionizing radiation. Particular attention is given t o a study of sanpling methods f o r obtaining the gonad dose of patients receiving medical exposure, Hawever, the methods recommended here could be extended i n order t o make an estimate of the dose received by other organs of interest, e.g., the bone rna,rrow and the lens of t h e eye. i n applying these methods t o a study of occupa,tional exposure t o medical sources of radiation, but a number of modificatAons would be required i f the survey were extended t o include a study of other types of occupational exposure, e.g., industrial radiography, X-ray analysis, X-ray diffraction, etci. There would be very f e w additional problems I n some cases there is tu1 overlap of this report w i t h discussions of other task that could be applied i n estima1;ing the gonad dose from skin dose measurements and from d a t a on the 'type of exposure, the X-ray techniques used, and information about the characteristics of the patient. which i s considering the problems associated with sending a questionaalre t o professional TbLs is particularly tiwe with reference t o Task I which i s reporting on methods Also, there is considerable overlap i n the case of Task N c., Several questions are raised which must be answered before f a 1 reconmendations can be made relative to what appear t o be preferred sampling methods. tions are as follows: 1- Is it desired t o determine the genetically significant dose from ionizing radiation Some of these questhat the present population has received? that children conceived today will accumulate during t h e i r reproductive period i f present exposure conditions continue unchanged? or that children conceived today will accMnilate during their reproductive period i f the present trend of increasing exposure t o ionizing radiation continues unabated throughout their reproductive life ? 2 - Is it desired t o choose the single sampling method that would be most applicable t o a l l countries or should several methods be recommended and each be applied where 3 - Is the recammended sampling method (a) t o be used only once i n a single world-wide survey t o obtain the presently existing, genetically significant, average gonad dose for each intermarrying

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(b) .to be applied over a continuing period i n order t o keep track of the genetically significant group exposures? o r t o be applied conti.nuously i n order t o control individual exposures i n addition t o serving as a means of collecting group data of genetic

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Although on first thought one might be tempted t o recommend direct measurement and recording of the exposure t o ionizing radiation received by each and every person i n the population, a study of the stupendous problems involved and high costs leads one very quickly t o consider seriously the more immediately possible and practical methods of sampling the exposure received by a small segment of the population. of placing a dosimeter on every person in the population would be: The principal advantages (1) The dosimeter, if properly used, provides information useful in estimating the accumulated dose t o various organs of the body and helpful in the prevention of overexposure to the individual. t o be more alert in avoiding unnecessary exposure t o ionizing radiation. If the meter is worn at all times by each person, it could provide a means of estimating exposure during emergency conditions resulting from radiation accident:; or military use of atamic weapons. of the disadvantages of placing dosimeters on every person i n the population It should cause a person The cost of the meters, t h e i r servicing and calibration, and of reporting and maintaining the records of dose would be very great. In many cases the patient, rather than the doctor, would be inclined t o make the decisions relative t o the medical application of X-rays and 7-rays. Sometimes it i s desirable not t o inform a patient of his physical condition; the dosimeter record might reveal such information t o the patient. Unless appropriate meters were used properly, they would furnish data that is misleading and of ll t tle value. wide range of sensitivity; they would have t o be rugged, tamperproof, and convenient t o wear; they would have t o be worn at the proper location for each planned exposure t o ionizing radiation. In some cases the radiologist might hesitate t o give t o a patient equipped with a dosimeter what he considers t o be the required dose because of fear For a small fraction of the same expense and effort more accurate information could be obtained on the genetically significant dose by the appLication of sampling techniques rather than t o t a l population sampling. The meters would have t o have a Of course a record of the medical exposure from ionizing radiation received by the entire population would not require thata doslmeter be assimed t o each individual. t h i s information could be obtained directly from those administering the medical exposure

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by requiring that all medical sources of ionizing radiation be Jicensed and by specifflng that i n order t o retain such license, all medical exposures must be reported t o an appropriately designated central agency. readings, using appropriate ins1;ruments furnished the medical man, or they could be calculated from basic data furnished by Task 1. on an individual basis -- in wlsLch case it would serve some of the useful functions of an individual personnel monitoring program as outlined above -- o r it could be kept on an impersonal basis (no names of individuals f'urnished the central agency). many of the disadvantages listd above could be avoided but it would be more difficult to verify the accuracy and punctuality of the data f'urnished the central agency. The exposures so reported could be based on instrument The data could be kept by the central. agency In this Latter case After a review of some of the pros and cons w i t h reference t o direct measurement and recording of the exposure t o ionizing Mati on received by the entire population -- either individually or collectively -- it seems clear that although, perhaps eventually, a more comprehensive system of personnel monitoring o r auditing should be developed, it would be preferable t o proceed first with a less expensive, less complicated, and more immediately operative survey of' the radiation exposure received by a small but representative sample of the popubtion. as those of a universal survey except that if only 1/2$ of the t o t a l population is exarmned, the difficulties encountered are reduced almost by a factor of 200. assumed that unlimited funds etll not be available f o r W s survey and that best estimates of the significant genetic dose received by the population a t large can be obtained from a carefully planned and well directed survey of a representative sample of the population rather tham expending the same effort and Funds i n conducting a poorly planned and executed study of a larger population. Various Methods of Direct SampHng The problems of a sample survey are essentially the same In any case, it i s 1 - Poll of persons selected a t random or living in typical communities. b. by personal contact c. by furnishing instruments 2 - P o l l of medical men selected at random or practising i n typical communities. c. by furnishing instruments 3 - Poll of institutions selected a t random or located i n typical communities. b. by personal contact c. by furnishing instruments

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1 - Poll of Individuals i n a Sample of the Population Theoretically it would be desirable to poll all members of the population t o obtain information on exposure t o ionizing radiation but practically, because of limitations of cost and numbers of trained surveyors available, better results can be expected with the stye e f f o r t and cost from a poll of carefully selected, characteristic segments of the population. A poll of persons selected at random or of a l l individuals living i n communities selected a t random has ideally certain advantages over a poll at the sources of exposure. This results from the fact that it would be difficult to ascertain that a representative selection of physicians or institutions had been chosen for sampling. It would be difficult especially t o take into proper account the exposures given by such groups as private practitioners, chiropdists, chiropractors, etc. A p o l l of selected individuals i n the population could be accomplished by sending a questionnaire, (1a.), or by personal interview, (1b.), and could be carried out either with (1 c-) o r without instruments furnished t o the selected individua.ls. a. Poll by Letter It seems t o be the general concensus of the Task Leaders reporting from the various countries that a questionnaire sent t o individual people selected a t random in the popuhtion would be of l i t t l e or dubious mdue and most likely would not provide quantitative informizing radiation i n the recent past; a significant segment of the population does not distinguish between X-ray, diathernly, infrared and ultraviolet; and i f a person should recall the approximate dates of recent X o r 7-ray exposures, he most likely would not be able t o furnish reliable information regarding the nature of the exposures. is a large element of error in the knowledge of individuals concerning the correct name and address of the source of exposure. followed up with letters or preferably with visits t o the medical authorities that were thought t o have administered the exposure. might be obtained from questiorulaires sent t o representative samples of the population and the accuracy thereof cannot be determined without recourse to a pilot study or presurvey, but the response of a general population sample t o mailed questionnaires i s notoriously poor and is subject t o an extremely large element of bias. tionnaire survey would be t o se:Lect recipients who were representative of the population Many of those queried would not know whether they had had medical exposures t o ionIn any case, statements of exposure would have t o be The extent t o which even limited infornation The first step i n such a quespopulation, and some of the methods of selection have been tested and proven t o be of a measurable and acceptable accurxy. A survey by t h i s technique would involve the preparation of a questionnaire designed to elicit the desired information from all individuals i n Many methods have been developed f o r the selection of such a sample of the

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accuracythat carp be expected to result from such a survey. estimate as to t h e information tlhat could be obtained directly from a questionnaire to a sample of the papulation indicatles that no information beyond the presence or absence of exposure durbg a recent relatively short time interval, together w i t h information of undeterminate accuracy regar- the source of t h e exposure, would be forthcoming. study of a sample population by itself would not be expected to provide the desired information. A pilot study would yield some useful information regarding the distribution of exposure among various groupings of the population; it would furnish some data regarding the reliability of this type of survey; it would make it possible to arrive at a more reliable estimate of the cost of an extensive survey of this type; a d would aid in establishing the feasibility of giving further consideration to this method of obtaining the desired informD~ISthe questionnaire should be understandable to persons of all socialSince this is impossible, of course, the question is one of the degree of Therefore, the most optimistic b. Poll by Personal Contact This method differs froxo the letter poll, 1 a., in that contact with the selected individuals in the population would be made by personal interviews of trained surveyors who would call on the individuals and obtain ansuers to a questionnaire. Otherwise this method of sampling is encumbered with inany of the same difficulties and sources of error as the poll by letter. surveys, etc. have indicated that the overriding difficulties and complications of a mail sampling technique for the population have been so serious that, i n spite of the relative economy, this technique has been largely supplanted by surveys by trained interviewers making has been well established. Many years of mqerience of census bureaus, health surveys, vital statistic The accuracy to which data in general can be provided by this technique This method has advantages as follows: (1) A letter poll can be disposed of in the wastebasket more easily than a well mannered, tmined surveyor can be turned away from the door. The information desired in the questionnaire can be explained more clearly in a personal interview than by a general form letter. Information can be obtained in the personal interview that will aid in evaluating the accuracy of the data received. …