An investigation into the use of biokinetic models when assessing intakes of plutonium

Abstract

The goal of internal dosimetry is to assess the dose to an individual from an intake of a radionuclide. This usually encompasses assessing the intake amount based on some form of bioassay measurement used with a biokinetic model. There are many published biokinetic models that describe the transfer of radionuclides throughout the body. It would be beneficial at times if one could interchange certain biokinetic models with another to assess an intake based on bioassay data to save time and make calculations simpler. This research compared the daily excretion rates by interchanging widely used biokinetic models in different combinations. These model combinations were then used to assess an unknown intake of a case study. It was shown that the ICRP-30 and ICRP-66 respiratory tract models can only be interchanged at specific times post intake to give similar excretion results from an inhalation intake. It is feasible to interchange the ICRP-67 plutonium systemic model or the newer Luciani and Polig plutonium systemic model to assess an intake based on fecal bioassay data, but not urine bioassay data for ingestion intakes. It is not feasible to interchange the systemic models when assessing intakes from a wound or injection. Using different combinations of biokinetic models predicted intakes within 30% for a case study which included a relatively long inhalation chronic intake followed by a much shorter chronic inhalation intake. It was shown that the predicted initial chronic intake for each combination of models gave fecal excretion values which deviated the most from the worker's fecal bioassay data. This could mean that the biokinetic models yield inaccurate excretion rates for long chronic intakes.