A Review of the Dose Reconstruction Program of the Defense Threat Reduction Agency (2003) / Chapter Skim
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I. Introduction
I. Introduction
Pages 15-43
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From page 15... ...
In April 1998, the Senate Committee on Veterans Affairs held a hearing that focused on dose reconstruction and on issues regarding compensation for "atomic veterans." In August 1998, the committee released its hearing report and asked the General Accounting Office (GAO) to review all available information related to dose reconstruction to determine its reliability for measuring veterans' radiation exposures and to assess the completeness of historical records used to assign radiation doses.
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whether or not the assumptions made regarding radiation exposure based on the sampled doses are credible; and 4) whether or not the data from nuclear tests used by DTRA as part of the reconstruction of the sampled doses are accurate.
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Additional atmospheric test series in the Pacific were WIGWAM in 1955, HARDTACK Phase I in 1958, and DOMINIC Phase I in 1962. Additional atmospheric test series in Nevada were TEAPOT in 1955, HARDTACK Phase II in 1958, and DOMINIC Phase II in 1962.
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There have also been high-altitude, rocket-launched tests and tests of nuclear devices for peaceful uses in a program called PLOWSHARE. I.B.2 Radiation Exposures of Military Personnel In understanding the significance of radiation exposures of military personnel that resulted from their participation in the atmospheric nuclear-weapons testing program, it can be helpful to consider that these exposures were in addition to unavoidable exposures to natural background radiation that have been experienced by all personnel throughout their lives.
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From page 19... ...
However, such information can be helpful as each individual judges for himself the significance of his exposures during the testing program. The types and amounts of ionizing-radiation exposures received by military personnel participating in atmospheric nuclear-weapons test detonations depended on the characteristics of the detonation, the role of the participants, and the proximity of personnel to detonations and fallout of nuclear debris.
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The few exposed to neutrons from nuclear-weapon detonations, who were close to the blast, included pilots flying close to detonations to collect samples and volunteer officers in protective trenches at short distances selected to determine safety measures for other military personnel at different distances from detonations during a nuclear confrontation. The number of volunteer officers exposed during atmospheric nuclear-weapons tests was probably less than a few hundred.
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In addition to maneuver troops and observers, military personnel were exposed during performance of their support functions and monitoring activities. For example, pilots who took gaseous and particulate samples of clouds from nuclear detonations to be analyzed in determining yields were exposed externally to high levels of gamma radiation from the time they collected the samples until they left their aircraft.
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Throughout this report, we refer to this organization as the Department of Veterans Affairs although it is recognized that for the early period of the atomicveterans compensation program, Veterans Administration was the name of the agency. 2Although the dose reconstruction program for atomic veterans was initiated as a result of concerns that radiation exposure could have caused the unexpected increase in leukemia among participants at Shot SMOKY, the number of cases and the study population were both small, and the analysis by Caldwell et al.
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In 1983, it was decided to consolidate the teams at DNA and make procedures for dose reconstruction more consistent across the services. SAIC continued to perform dose reconstructions for DNA and eventually teamed with JAYCOR, which is responsible for confirming a veteran's status as a participant in the testing program and for developing historical background 4 The beginning effort to evaluate effects of atmospheric nuclear-weapons tests on atomic veterans was known as the Nuclear Test Personnel Review.
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It specified that atomic veterans were entitled to medical care if they could prove that their disease was service-connected, which few could do. The next law was PL 98-542, the Veterans' Dioxin and Radiation Exposure Compensation Standards Act of 1984, which listed in greater detail how such service connection was to be established.
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In such a case, however, the veteran's claim can be evaluated under the nonpresumptive regulation. The laws governing compensation for atomic veterans have continued to change over nearly two decades.
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Numbers of actual test participants were not well known during that study with the result that thousands of test participants were inadvertently omitted and thousands more military personnel who were not participants were included. An additional problem was the illness occurrences in the general populations as a comparison cohort, causing a "healthy soldier effect" that may have obscured illness in atomic veterans.
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The committee concluded that "the procedures used to estimate external radiation doses were reasonably sound." It also concluded that "if bias exists in the dose estimates, it is probably a tendency to overestimate the most likely dose, especially for internal emitters." Further discussion of the findings on methods of estimating dose from internal emitters is given in Section V.C.2. However, the National Research Council committee had difficulty in finding information that summarized the procedures being followed in the dose reconstruction process and recommended that DTRA develop a comprehensive report addressing the methods and procedures being used.
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I.C PRINCIPLES AND PROCESS OF DOSE RECONSTRUCTION I.C.1 Introduction to the Process of Dose Reconstruction Dose reconstruction refers to the process of estimating radiation doses that were received by individuals or populations in the past as a result of particular exposure situations of concern. For example, this report is concerned with radiation exposure of military personnel (the atomic veterans)
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The process of dose reconstruction for atomic veterans generally is similar to the process that has been used in other cases. Dose reconstructions may differ substantially in some respects, such as in the radionuclides, radiation types, and exposure pathways of concern; the types, quality, and quantity of information available for estimating doses; the degree to which modeling, rather than relevant measurements, must be used to estimate doses; and the importance of subjective judgment, both scientific and nonscientific, in estimating doses.
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I.C.2 Elements of Dose Reconstruction Process Regardless of the purpose of a dose reconstruction, the process has several basic elements, which the committee identifies as follows: Definition of exposure scenarios, Identification of exposure pathways, Development and implementation of methods of estimating dose, Evaluation of uncertainties in estimates of dose, Presentation and interpretation of results Quality assurance and quality control. Those elements constitute the basic principles of dose reconstruction.
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The committee emphasizes that no single approach to defining exposure scenarios is suitable in all cases. If activities of an atomic veteran were simple and indisputable and the radiation environment was well characterized, defining an adequate exposure scenario is usually straightforward.
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The task of defining exposure scenarios is the most important part of the dose reconstruction process for atomic veterans. An assumed exposure scenario provides the basis of an estimate of dose, so the adequacy of an estimated dose for purposes of dose reconstruction can be no better than the validity of the assumed scenario.
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The importance of different pathways of external exposure depends on the exposure scenario. For example, external exposure to radionuclides deposited on the ground or other surfaces often is the most important pathway of external exposure at the NTS and in the Pacific.
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The most likely pathway of ingestion exposure of atomic veterans involved inadvertent ingestion of contaminated material that originated in soil or on surfaces. However, ingestion may have occurred otherwise in unusual circumstances, for example, if a person consumed food or water that had been directly contaminated by fallout, or if a person on a residence island in the Pacific consumed local terrestrial foodstuffs that were contaminated by fallout or root uptake of fallout radionuclides from soil or consumed contaminated seafood obtained from local waters.
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For example, estimates of dose to atomic veterans due to inhalation of fallout that was resuspended in the air from the ground or other surfaces must be based on models to estimate concentrations of specific radionuclides on the surface and the extent of resuspension, because radionuclide concentrations on surfaces or in air generally were not measured during periods of exposure. The dosimetric quantity calculated in dose reconstructions generally is the biologically significant radiation dose to organs and tissues of humans.
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. This approach is particularly appropriate in dose reconstructions for atomic veterans because veterans are to be given the benefit of the doubt in estimating doses used to evaluate claims for compensation for radiation-related diseases (see Section I.C.3.21.
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For example, the interpretation of results generally would depend on whether the purpose of the dose reconstruction is to provide best estimates of the dose to a specific person, best estimates of dose to a representative person in a group, upper-bound estimates of dose to persons or groups, or assurance that the dose received by a specific person or representative person did not exceed a specified value. As discussed throughout this report, the proper interpretation of results of dose reconstructions for atomic veterans is in terms of obtaining credible upperbound estimates of dose to individuals.
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I.C.3 Special Aspects of Dose Reconstructions for Atomic Veterans Three other aspects of dose reconstructions for atomic veterans warrant special consideration. First, dose reconstructions have been used to evaluate claims for compensation by specific persons who incurred a disease that could have been caused by exposure to ionizing radiation during the atomic-testing program; in many cases, estimates of dose to a particular organ or tissue in which a cancer or other disease has occurred are compared with a specified dose as part of the process of deciding whether the disease was at least as likely as not to have been caused by radiation exposure (see Section III.E)
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However, dose reconstructions for atomic veterans focus on estimating actual doses to specific persons. It is important that uncertainties in standard models used in radiation protection be acknowledged and properly taken into account in dose reconstructions for specific veterans in the context of a compensation program.
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Ideally, consistent approaches to developing exposure scenarios and consistent methods of estimating doses would be used in dose reconstructions for all atomic veterans. For example, if a bias toward overestimation of dose was deliberately included in some dose reconstructions (for example, on the basis of benefit of the doubt)
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From page 41... ...
Similarly, new measurement techniques, such as electron paramagnetic resonance, can be used to estimate accumulated radiation dose in tooth enamel (for example, see Romanyukha et al., 2000, 2002~. Such developments should be followed, although they may be limited in their sensitivity to the low radiation doses that were received by most atomic veterans and, thus, may provide only limited data of use in evaluating veterans' claims for compensation.
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From page 42... ...
Although that concern seemed to be somewhat peripheral to our scope, it is indirectly related because knowledge about the "accuracy" of the doses, as stated in the committee's charge, could affect decisions about compensation. The veterans have been led to believe that over the course of the compensation program, relatively few claims have been awarded under the nonpresumptive regulation even though more than 4,000 dose reconstructions have been performed.
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I INTRODUCTION 43 doses, the issue continues to cause considerable confusion among the atomic veterans, which the committee hopes to alleviate. Some of the concerns expressed by the atomic veterans are beyond the scope of this study, but the committee has endeavored to answer as many of them as possible in the report and appreciates the veterans' willingness to express their concerns to us throughout the project.
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