Draft report: Specific Absorbed Fractions for Reference Paediatric Individuals
Abstract
The calculation of doses to organs and tissues of interest due to internally emitting radionuclides requires knowledge of the time-dependent distribution of the radionuclide, its physical decay properties, and the fraction of emitted energy absorbed per mass of the target. The latter property is quantified as the specific absorbed fraction (SAF). This document provides photon, electron, alpha-particle, and neutron (for nuclides undergoing spontaneous fission) SAF values for the suite of reference individuals.
The reference individuals are defined largely by information provided in Publication 89. Some improvements and additional data are provided in this publication which define the reference individual’s source and target region masses used in the Occupational Intake of Radionuclides (OIR) and Dose Coefficients for Intakes of Radionuclides by Members of the Public (EIR) series of publications. The set of reference individuals includes males and females at ages of 0y (newborn), 1y, 5y, 10y, 15y, and 20y (adult). The reference adult masses and SAFs provided in this publication are identical to those in Publication 133 and those used in the OIR series of publications.
Computation of SAF values involves simulating radiation transport in computational models which represent the geometry of the reference individuals. The reference voxel phantoms of Publication 143 are used for photon and neutron transport and most of the electron transport. Alpha particle transport is not necessary for large tissue regions as the short range allows for an assumption of full energy absorption (absorbed fraction of unity) for self-irradiation geometries. Additional computational models are needed for charged particles in small, overlapping or interlaced geometries. Stylised models are described and used for electrons and alpha particles in the alimentary and respiratory tract regions. For charged particles within the skeleton image-based models are used to compute SAFs.
This publication is accompanied by an electronic supplement which includes files containing SAFs for each radiation type in each reference individual. The supplement also includes source and target region masses for each reference individual, as well as skeletal dose response functions for photons incident upon the skeleton.