Dosimetry for Epidemiological Studies: Learning from the Past, Looking to the Future
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Dosimetry for Epidemiological Studies: Learning from the Past, Looking to theFutureAuthor(s): Steven L. Simon, Andr Bouville, Ruth Kleinerman, and Elaine RonSource: Radiation Research, 166(1):313-318. 2006.Published By: Radiation Research SocietyDOI: http://dx.doi.org/10.1667/RR3536.1URL: http://www.bioone.org/doi/full/10.1667/RR3536.1
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RADIATION RESEARCH 166, 313318 (2006)0033-7587/06 $15.00q 2006 by Radiation Research Society.All rights of reproduction in any form reserved.
Dosimetry for Epidemiological Studies: Learning from the Past,Looking to the Future
Steven L. Simon,1 Andre Bouville, Ruth Kleinerman and Elaine Ron
Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
Assembling the suite of manuscripts for this special issueof Radiation Research has afforded us a unique opportunityto evaluate the various methods of dosimetry used in sup-port of epidemiological studies as well as the strengths andweaknesses of different dosimetric approaches. Of equalimportance is having the opportunity to highlight elementsof dosimetry that are especially important to conductingconvincing epidemiological studies.
In general, analytical epidemiological studies of radiationeffects attempt to combine information on disease (e.g. can-cer) occurrence with estimates of radiation dose to individ-uals such that the relationship between the increase in dis-ease incidence compared to the background rate as a func-tion of the true dose can be described. With regard to thelanguage and science of dosimetry, there are a number ofterms, assumptions and implied meanings that are often notclear to the variety of scientists involved in radiation epi-demiology studies. This issue should help inform these re-searchers.
In this special issue of Radiation Research devoted tothe dosimetric aspects of radiation epidemiology, we at-tempted to clarify what is meant by dosimetry for epi-demiological studies, what is required to ensure that thefindings of dosimetry-based epidemiological studies are ascredible and generalizable as possible, and to give practicalexamples from current or recent studies. While this collec-tion of papers certainly does not cover all of the aspects ofdosimetry in epidemiology, it is meant to describe wherewe have been in terms of applying dosimetry for epide-miological purposes and where we are going to further ad-vance the discipline.
SUMMARY OF STUDIES PRESENTED
Readers of this issue of Radiation Research are probablyalready acquainted with a wide range of dosimetric meth-
1 Address for correspondence: Division of Cancer Epidemiology andGenetics, National Cancer Institute, 6120 Executive Blvd., Room 7100,Bethesda, MD 20892; e-mail: firstname.lastname@example.org.
ods. Here we briefly summarize the principal identifyingcomponents of the ten applications of dosimetric methodsdescribed in the individual papers. Table 1 contains a listingof the papers and a greatly abbreviated description of themethods employed and the available input data.
Methods for estimation of organ doses after the admin-istration of radioisotopes as described by Brill et al. (1) arewell developed and have depended for several decades onthe formulations of the Medical Internal Radiation Dose(MIRD) Committee [see ref. (2) for a primer on those meth-ods]. The basis for dose estimation by these methods is ametabolic model coupled with a measured amount of ad-ministered radioactive material. Unlike occupational andenvironmental dose estimations, the great advantage inthese situations is that the amount of activity administeredis usually known. Though the ability to accurately measurethe administered activity does not pose any great technicalchallenges, differences between individuals in their metab-olism (kinetics) and anatomy (size and exact location oforgans) lead to uncertainties in the absorbed dose for anyidentified person. Thus, even when activity intake is known,doses cannot be estimated with absolute precision. One ofthe limitations in estimating individual dose arises from theuse of standardized or mathematical phantoms that are as-sumed to representing the individual receiving the treatmentdose.
Even iodine-131, one of the most studied nuclides forwhich kinetics in the human body has been described sincethe early 1950s (3), has dose uncertainties, partly becauseof human variation, but also due to secular changes in thedietary component of stable iodine. Changes in iodine in-take have occurred at the local, national and internationallevels, and these can affect the amount of radioiodine ab-sorbed by each individual thyroid gland.
Estimation of doses from medical procedures, includingtreatments and diagnostic procedures, as described by Sto-vall et al. (4), involves traditional treatment planning tech-niques, archival data collection, and contemporary mea-
TABLE 1Summary of Physical or Calculation-Based Dosimetric Methods Described in Publications of this Issue
Exposure setting, population,and location
Organs/tissues fordose estimation
Mode of exposure(internal, external)
Primary methods andinput data
Brill et al. (1) Clinical: patients (emphasis onU.S.)
Thyroid primarily Internal (131I) Metabolic model using measuredadministered radionuclides
Stovall et al. (4) Clinical: patients (emphasis onU.S.)
All organs 1 redbone marrow(RBM)
External and internal Measurements and calculationsbased on records from admin-istered treatments and/or diag-nostic tests
Bouville et al. (6) Reactor: clean-up workers(Ukraine)
RBM primarily, in-ternal (minor)
External primarily,internal (minor)
Film badge measurements (indi-vidual or group), exposurerate, questionnaire responses
Gilbert et al. (7) Various reactors: workers (U.S.,Europe)
Whole-body External primarily Film badge and other dosimetermeasurements
Simon et al. (8) Clinical: radiologic technolo-gists (U.S.)
All organs, emphasison breast, skin,RBM
External Film badge measurements, ques-tionnaire responses, historicalliterature
Beck et al. (9) Public: population living down-wind of nuclear test sites(U.S., Kazakhstan, MarshallIslands)
Thyroid primarily,also RBM
External and internal Measurements of exposure ratecoupled with environmentaltransfer models, questionnaireresponses
Cullings et al. (12) Public: A-bomb survivors (Hi-roshima and Nagasaki, Japan)
Whole-body External Reconstruction of detonationconditions (source term), geo-graphic location, house con-struction
Degteva et al. (11) Public: people living near con-taminated river (Chelyabinsk,Russia)
All organs 1 RBM External and internal Release data and environmentaltransfer model
Likhtarev et al. (10) Public: people living nearChernobyl reactor (Ukraine,Belarus)
Thyroid External and internal Measurements of 131I in thyroidplus model
Puskin et al. (15) Homes and mines (internation-al)
Lung Internal by inhala-tion
Physics based model to convertfrom exposure to dose, depen-dent on environmental mea-surements of 222Rn
surements, sometimes of aged radiation-generating ma-chines. The goal of those various techniques is, in general,to characterize the dose to organs/tissues outside of treat-ment areas, primarily due to within-body scatter of radia-tion and leakage from the treatment machine. Various typesof phantoms are used for dose measurements and dose es-timation, including mathematical, anthropometric and waterphantoms. Therapy doses are particularly amenable to re-construction because, much like when radiopharmaceuticalsare administered, the irradiation conditions were controlledand the dose to the treatment site was recorded, althoughdetailed radiation records are not always accessible (5).Since patients comprise the largest population group ex-posed to doses ranging from very low to extremely high,dosimetry and risk associated with those exposures willcontinue to be a major focus of study.
Occupational exposure includes a wide range of job de-scriptions in the medical, weapons construction, and nucle-
ar power industries, and dosimetric methods reflect thosevarious conditions.
Dose estimation for the Chernobyl clean-up workers asdescribed by Bouville et al. (6) took advantage of theunique exposure conditions that could be assumed as rela-tively homogeneous over the body. In that study, doseswere estimated by one of four different methods, dependingon the individual study subject and the data available forthat subject: individual film badge measurements, a groupfilm badge measurement, group assessment based on thedose rate at the work assignment location, or individualreconstruction based on time spent at different locationstaking into account the respective dose rates at those lo-cations. The doses for the Estonian workers were also es-timated by biodosimetric methods, but neither GPA norFISH was able to detect any biological changes comparedto control subjects. The failure of biodosimetry to supportestimated doses was likely related to the overestimation ofrecorded doses for those exposed workers as well as the
limits of detection. Nuclear workers, in the context of thepaper by Gilbert et al. (7), include personnel involved inweapons production, nuclear power generation, and relatedresearch activities in the U.S., UK and Canada. Studies ofthose workers encountered some of the same problems asthe study of radiological technologists (8) in that workerswere monitored over time (from the 1940s through recentyears) when the calibration methods for personnel moni-toring badges were evolving. In addition to different typesof calibrations, dosimeters used early in the profession didnot respond accurately to all radiation energies or uniformlywith direction. Gilbert and colleagues (7) primarily char-acterize the bias and uncertainties related to the dosimetryand describe some ways to account for the uncertainty sothat doseresponse analyses are not unnecessarily limited.
Radiation technologists began to be needed in the earlypart of the 20th century during the developmental periodof diagnostic and therapeutic radiology. Throughout the20th century, the responsibilities of these medical profes-sionals changed from a mixture of all tasks in a radiologydepartment to becoming more specialized in specific pro-cedures. Over that same period, understanding and recog-nition of radiation risks, development of ALARA (as lowas reasonably achievable) principles, and improved tech-nologies served to reduce the doses per individual proce-dure to the patient and the technologist. At the same time,the workload of technologists has increased due to thewidespread use of radiological procedures in medicine. Es-timation of doses to medical workers rarely goes beyond areported value of the personal dose equivalent, a regulatoryquantity derived directly from a calibrated film badge. Inthe dosimetric methods described by Simon et al. (8), as-sumptions based on literature review were used to describethe nature and quality of radiation fields to which individualtechnologists were exposed, thus allowing for estimation oforgan doses and their uncertainties. For reconstruction ofdoses to radiation technologists, responses to detailed ques-tionnaires were used as well as large national databases offilm badge readings that included data on members of thecohort.
The estimation of doses from exposure to radioactivefallout from nuclear weapons tests and from releases ofradionuclides to the environment occupies a special nichein dosimetric applications because it includes a wide varietyof disciplines including physics, environmental science,anatomy and physiology, and even human behavior.
There are several unique qualities of fallout dosimetry.First was the large number of source terms; between 1945and 1980, over 500 weapons tests were conducted in theatmosphere at a number of locations around the world. An-other unique quality of fallout studies is that individual do-simetry data, except occasionally for military personnel, arenever available. Even for military personnel, monitoring
data would apply only to external exposures, and falloutdose estimation usually includes internal exposure as well.Hence dose estimation for fallout exposure almost alwaysrequires the use of complex models with numerous param-eters. To characterize those parameters, only very limitedamounts of real data are typically available, resulting inhigh uncertainty, particularly for internal dose. Second, thelong interval since the exposures occurred has resulted inloss of some original data, although the sparse historicalmeasurement data available are generally sufficient to es-timate external exposure doses reasonably well. Recon-struction of internal doses from ingestion and inhalation ofradionuclides is significantly more complex and is almostalways more uncertain than for external dose estimation.Internal dose estimates are typically based on estimates ofthe ground deposition per unit area of specific radionuclidesand subsequent transport of radionuclides through the foodchain whereas, for external dose estimation, reconstructionis reasonably straightforward and relevant data in the formof exposure rates are often available.
In the description of fallout dosimetry methods by Becket al. (9), the number of locations for which dose estimateshas been made is impressive and covers most of the con-tinents as well as some island locations. Moreover, becauseof the large numbers of measurements of fallout radionu-clides in the environment and in humans, fallout studieshave been some of the most innovative in terms of devel-oping individual dose and uncertainty estimates.
Despite nearly 50 years of study, technical challenges infallout dosimetry still remain. These include needed im-provements in modeling of radionuclide fractionation with...