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IV.C.2.2.4 Summary of inhalation dose coefficients used in dose reconstructions
All dose coefficients for inhalation of radionuclides used in dose reconstructions for atomic veterans are based essentially on dosimetric and biokinetic models developed in ICRP Publication 30 (ICRP, 1979a) and are given in documentation of the FIIDOS computer code (Egbert et al., 1985). The dose coefficients assume that inhaled radionuclides are in oxide form and, in all cases of inhalation of alpha-emitting radionuclides, assume a biological effectiveness of alpha particles of 20 relative to photons and electrons.
In estimating inhalation doses to atomic veterans, an analyst must choose between dose coefficients calculated by the ORNL group (Killough et al., 1978a; Dunning et al., 1979) and values calculated by ICRP (1979a; 1979b; 1980a; 1981a; 1981b; 1982a; 1982b). There are some differences in inhalation dose coefficients in the two data sets, but the committee is not aware of any written policy in the NTPR program to guide the choice. An analyst also must choose inhalation dose coefficients based on an assumed particle size (AMAD) of 1 or 20 μm. With some exceptions that are based on reasoned arguments, the stated policy is that the particle size that gives the higher estimate of dose to the organ or tissue of concern will be used (Schaeffer, 2002b).
Inhalation dose coefficients used by the NTPR program are not intended to overestimate doses that would result from given intakes of radionuclides of known particle size and solubility. In using these dose coefficients, only the assumed particle size could result in substantial overestimates of inhalation dose to particular organs or tissues. Thus, as emphasized in Section IV.C.2.1.7, the NTPR program, in its effort to obtain “high-sided” estimates of inhalation dose, relies primarily on assumptions that are intended to result in overestimates of airborne concentrations of radionuclides to which participants were exposed, especially assumptions about resuspension factors that are applied to deposited fallout or neutron-activation products in surface soil.
IV.C.3Methods of Estimating Ingestion Dose
When ingestion of radionuclides is assumed to occur, such as by consumption of food or water contaminated by fallout, equivalent dose to an organ or tissue of concern is calculated by using an estimated activity of each radionuclide ingested and the appropriate ingestion dose coefficient. Dose coefficients are obtained either from ORNL reports (Killough et al., 1978a; Dunning et al., 1979) or from ICRP Publication 30 (ICRP, 1979a; 1979b; 1980a; 1981a; 1981b; 1982a; 1982b). The latter set of dose coefficients also is given by Eckerman et al. (1988).
Ingestion of radioactive materials apparently is considered only rarely in dose reconstructions for atomic veterans. The one case encountered by the committee concerned a small group of participants on Rongerik Atoll in the Marshall Islands who were exposed to very high levels of fallout after Operation CASTLE,