the doubt suggest the possibility of a much higher credible upper bound of the dose to an individual than reported by the NTPR program, even when the dose is based primarily on film-badge data. Upper-bound estimates of external dose should include consideration of the possibility of incorrect exposure scenarios, possibly missing or erroneous film-badge data, the impact of limited survey data, and other such factors. To give the veteran the required benefit of the doubt, some method should be devised to increase upper-bound estimates of external dose when there is reason to believe that any of those events may have occurred.
The committee has concluded that, contrary to claims by the NTPR program, calculated internal doses from inhalation are not always “high-sided.” The committee has identified scenarios for which the method used by the NTPR program to estimate inhalation dose probably provides credible upper bounds (95th percentiles of possible doses or above). However, the committee has also identified important scenarios for which estimates of inhalation dose obtained by the NTPR program probably underestimate upper bounds by as much as a factor of 100 or more. Furthermore, organ equivalent doses could be substantial in some of those cases.
The committee found that beta doses to the skin and lens of the eye, although claimed by the NTPR program to be “high-sided,” may not represent a credible estimate of the 95th percentile beta dose. Furthermore, beta doses from direct contamination of skin or clothing apparently have not been considered in dose reconstructions in any cases in which a veteran filed a claim for skin cancer.
The committee believes that upper bounds of neutron doses reported by the NTPR program are not credible, because of neglect of the uncertainty in the biological effectiveness of neutrons. When neutron doses were important, estimated upper bounds of the combined gamma-plus-neutron doses obtained by the NTPR program may be low by as much as a factor of 5.
The committee thus has concluded that the external gamma and neutron dose upper bounds and “high-sided” internal and beta skin and eye doses reported by the NTPR program often do not represent a credible estimate of the 95th percentile upper bound of the possible dose to an individual participant.
As discussed in Section III.E, VA uses the sum of the reported external-dose upper bound and organ internal dose to evaluate the probability of causation of a claimed radiation-related disease. By using the upper-bound dose estimate to evaluate probability of causation, rather than the best (central) estimate, VA intends to give the veteran the benefit of the doubt. However, to the extent that the reported doses do not provide credible estimates of 95th percentile upper bounds of organ total equivalent doses, evaluations of probability of causation may be less favorable to the veteran than intended. Implications of the committee’s findings with regard to evaluating claims for compensation are discussed further in Section VI.F.