Basis for the ICRP's updated biokinetic model for systemic astatine

The International Commission on Radiological Protection (ICRP) recently updated its biokinetic models for workers in a series of reports called the OIR (occupational intakes of radionuclides) series. A new biokinetic model for astatine (At), the heaviest member of the halogen family, was adopted in OIR Part 5 (ICRP in press). Occupational intakes of radionuclides: Part 5). This paper provides an overview of available biokinetic data for At; describes the basis for the ICRP's updated model for At; and tabulates dose coefficients for intravenous injection of each of the two longest lived and most important At isotopes,²¹¹At and²¹⁰At. At-211 (T_1/2= 7.214 h) is a promising radionuclide for use in targetedα-particle therapy due to several favourable properties including its half-life and the absence of progeny that could deliver significant radiation doses outside the region ofα-particle therapy. At-210 (T_1/2= 8.1 h) is an impurity generated in the production of²¹¹At in a cyclotron and represents a potential radiation hazard via its long-lived progeny²¹⁰Po (T_1/2= 138 days). Tissue dose coefficients for injected²¹⁰At and²¹¹At based on the updated model are shown to differ considerably from values based on the ICRP's previous model for At, particularly for the thyroid, stomach wall, salivary glands, lungs, spleen, and kidneys.