Inhalation dose coefficients used in all dose reconstructions were calculated based essentially on dosimetric and biokinetic models described in ICRP Publication 30 (ICRP, 1979a; 1979b; 1980a; 1981a; 1981b; 1982a; 1982b). In some dose reconstructions, inhalation dose coefficients are those given in the ICRP Publication 30 reports; these dose coefficients also are given by Eckerman et al. (1988). In many dose reconstructions, however, inhalation dose coefficients were obtained from Oak Ridge National Laboratory (ORNL) reports (Killough et al., 1978a; Dunning et al., 1979). The models used to calculate inhalation dose coefficients in the ORNL reports (Killough et al., 1978b) are in many respects the same as the models described in ICRP Publication 30. In particular, the model of the behavior of inhaled radionuclides in the respiratory tract is the same.
However, there are differences between the two models. For example, the behavior of radioactive decay products in the body is treated differently. In the ORNL models (Killough et al., 1978b), radioactive decay products that are produced in the body after intakes of a parent radionuclide are assumed to behave according to the biokinetic model for the decay product, whereas in the ICRP models (ICRP, 1979a), decay products that are produced in the body are assumed to behave according to the biokinetic model for the parent. Also, for some radionuclides, there are differences in parameter values used in the biokinetic models. For example, the fraction of ingested plutonium absorbed in the GI tract used in the ORNL calculations (Dunning et al., 1979) is a factor of 3 higher than the value assumed by ICRP (1979a). The same difference occurs in dose coefficients for organs or tissues other than those in the GI tract when plutonium is directly ingested or inhaled plutonium is swallowed.
The committee is not aware of any written policy in the NTPR program to assist an analyst in choosing between ICRP and ORNL dose coefficients for use in dose reconstructions for atomic veterans; both sets of data are included in the FIIDOS computer code (Egbert et al., 1985) and are readily available. Nor did the committee find explanations for choosing one data set over the other in dose reconstructions for individuals or participant groups.
In selecting inhalation dose coefficients from the ORNL or ICRP reports, several assumptions about conditions of exposure and other factors are required, including the size of inhaled particles, chemical form of inhaled radionuclides, and biological effectiveness of alpha particles relative to that of photons and electrons. Assumptions used in dose reconstructions for atomic veterans are described below.
Inhalation dose coefficients used in dose reconstructions for atomic veterans assume that inhaled radionuclides are attached to particles. The size of inhaled particles is specified by a quantity called the activity median aerodynamic diameter (AMAD). In any inhaled materials, there is a distribution of particle sizes