Electron specific absorbed fractions for the ICRP family of mesh-type reference computational phantoms

To provide electron specific absorbed fractions (SAFs) using the mesh-type reference computational phantoms (MRCPs) developed by the International Commission on Radiological Protection (ICRP).

The ICRP family of MRCPs from Publications 145 and 156 supersedes the voxel-type reference computational phantoms (VRCPs) used in ICRP Publications 133 and 155. Unlike the VRCPs, the MRCPs can explicitly define micrometer-scale radiosensitive target tissues and include intra-organ blood content. Electron SAFs were computed for all 12 MRCPs using the PHITS Monte Carlo code, covering 86 source regions and 62 target regions. Total electron SAFs were obtained using a component-based method that separates collisional and radiative contributions, with the latter derived from our companion photon SAF datasets. Results for the adult male MRCP were independently verified against Geant4 calculations.

The MRCP-based electron SAF datasets showed agreement with ICRP Publications 133 and 155 for self-absorption geometries across the full energy range. For crossfire geometries, differences were observed and are likely attributable to several factors, including revised organ geometries, the representation of micrometer-scale target tissue layers, the use of different photon datasets for the radiative SAFs, and differing low-energy extrapolation methods. Age-dependent trends were observed, with younger reference individuals often yielding higher SAF values. General agreement was observed between PHITS and Geant4 across the full energy range and source-target combinations considered.

To the authors' knowledge, this is the first study to provide complete electron SAF datasets spanning all ICRP MRCPs with expanded source-target combinations.