1980). The belief that the estimated doses are upper bounds is based on consideration of two assumptions used in the analysis. First, the assumption that a person spent 8 h d−1 in the most contaminated area for the entire period of occupation by the person’s unit should overestimate actual exposures because the area of maximum contamination was only about 1% of the entire area occupied; this assumption probably results in an overestimate of dose by at least a factor of 2. Second, it is highly unlikely that units were stationed near the Nishiyama Reservoir over the entire period; this assumption probably results in an overestimate of dose by a factor of about 10.

The results in Table IV.D.1 indicate that the maximum estimated dose was received by the 2nd Division Artillery Group in Nagasaki; the estimated external dose is 0.63 rem, and the estimated 50-year committed internal dose to bone is 0.65 rem, with lower internal doses to other organs. Again, those estimates are expected to be upper bounds of actual doses. At Hiroshima, the maximum dose occurred near ground zero. At that location, the estimated upper-bound external dose is 0.03 rem, and estimated internal doses are less than 0.005 rem. Thus, occupation forces in Hiroshima experienced little radiation exposure.

The results of the generic assessment by McRaney and McGahan (1980) described above and summarized in Table IV.D.1 represent upper-bound estimates of dose to participants who were exposed in Japan. However, when a participant files a claim for compensation or requests a dose reconstruction, an individualized dose reconstruction is often performed, based on knowledge of the participant’s times of exposure, locations, and activities. Doses assigned in individual dose reconstructions often are substantially lower than upper bounds obtained in the generic assessment.

IV.E METHODS OF ESTIMATING OR ACCOUNTING FOR UNCERTAINTY

The following sections consider the methods used in the NTPR program to estimate or otherwise take into account uncertainty in exposure scenarios and in estimates of external and internal dose. Consideration of uncertainty in all aspects of a dose reconstruction is important when the veteran is to be given the benefit of the doubt and the policy of the NTPR program is to obtain credible upper-bound estimates of dose.

IV.E.1 Uncertainty in Exposure Scenarios

Uncertainty in exposure scenarios is inherently difficult to quantify, especially uncertainty in a veteran’s activities and locations of the activities during periods of potential radiation exposure. When uncertainty in a veteran’s activities involves two or more specific choices, such as two well-characterized ships that the veteran might have been on during a given interval of time, the veteran



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