tion available to the committee. Similar judgments are required in performing dose reconstructions. Since it is not possible to determine exactly what happened to the veterans, the committee’s view is that the goal of dose reconstruction is to develop plausible assumptions that yield credible upper-bound estimates of dose, consistent with the requirement to give the veterans the benefit of the doubt.

The committee’s conclusions are divided into two groups: those answering the four questions posed in the statement of task; and those related to the establishment of continuing review and oversight of the program. Finally, the committee offers some additional explanation about the implications of its findings.

VII.A RESPONSES TO QUESTIONS IN COMMITTEE’S CHARGE

Chapter II describes the committee’s difficulty in understanding the intent of some of the questions that were presented in its charge and explains its interpretation of these questions. The questions in the statement of task, the committee’s interpretation of the questions, and responses to the questions are presented below.

Question 1. Is the reconstruction of the sample(d) doses accurate? {Because dose reconstruction is inherently uncertain, the committee interprets this question to be whether uncertainty in the sampled doses has been appropriately considered and whether credible upper bounds of doses to atomic veterans have been obtained.}

According to the regulations and the objectives of the NTPR program, the goal is to report at least the 95th percentile upper bound of possible doses for each veteran. The committee has concluded, however, that upper-bound doses from external gamma, neutron, and beta exposure are often underestimated, sometimes considerably, particularly when doses are reconstructed as opposed to being based on film-badge data. A number of findings led the committee to that conclusion. Some of these are described below.

Methods used by the NTPR program to estimate average doses to participants in various military units from external exposure to photons (mainly gamma rays) and neutrons are generally valid. However, because the specific exposure conditions for any individual often are not well known and the available measurements used as input to calculation models are sparse and highly variable, the resulting estimates of total dose for many participants are highly uncertain.

Film-badge data, if available, are considered the dose data of record. The dose inferred from a film-badge reading is estimated by using “high-sided” assumptions. However, in some cases, even film-badge data are more uncertain than reflected by the corresponding upper-bound estimates.

Although it is difficult to define the degree of underestimation of credible upper bounds of reconstructed external gamma doses, the committee has con-



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