Evaluating the reliability of biokinetic and dosimetric models and parameters used to assess individual doses for risk assessment purposes

The National Council on Radiation Protection and Measurements (NCRP) is in the final stages of preparation of a document discussing the reliability of biokinetic and dosimetric models and parameters used to assess individual doses for risk assessment purposes. An effort is made in the NCRP document to identify the strengths and weaknesses of the currently used biokinetic and dosimetric models, to evaluate the main causes of uncertainty associated with important parameters and to show, by way of examples, how an uncertainty analysis can be carried out. It is recognised, however, that most of the information available to conduct a detailed quantitative analysis relates only to a few radionuclides and that many gaps have to be filled in a subjective manner. As an exercise, members of the NCRP group were asked to estimate in a subjective manner the reliability of the dose coefficients published in ICRP Publication 30 for a list of about 20 radionuclides commonly associated with nuclear facilities. For each radionuclide, the chemical form was specified and two populations were considered: (1) healthy adult males, and (2) special groups expected to receive higher doses per unit intake than the average. According to the information provided by the members of the NCRP group, the effective dose received by most healthy males should be within a factor of 10 of the ICRP 30 value for most radionuclides and within a factor of 20 for special groups. This paper summarises the main issues that are discussed in the NCRP document with respect to the identification and application of procedures for the assessment of the reliability of dose coefficients for estimation of risks to individuals.