S-values estimation of positron-emitting radionuclides in the ICRP voxel-based adult male organs using a new Geant4-based code DoseCalcs: validation study

Identifying the organs and tissues at risk from internal radiation exposure caused by radiopharmaceuticals requires determining the absorbed dose. The absorbed dose for radiopharmaceuticals is calculated by multiplying cumulated activity in source organs by the S-value, a crucial quantity that connects the energy deposited in the target organ and the emitting source one. It is defined as the ratio of absorbed energy in the target organ per unit of mass and unit of nuclear transition in the source organ. In this study, we used a new Geant4-based code called DoseCalcs to estimate the S-values for four positron-emitting radionuclides ( ^11 C, ^13 N, ^15 O, and ^18 F) using decay and energy data from International Commission on Radiological Protection (ICRP) Publication 107. Twenty-three regions were simulated as radiation sources in the ICRP voxelized adult model developed in ICRP Publication 110. The Livermore physics packages were tailored to radionuclide photon mono-energy and β -mean energy. The estimated S-values based on β -mean energy show good agreement with those in the OpenDose data whose values were calculated using the full β spectrum. The results provide new S-values data for selected source regions; hence, they could be used for comparison and adult-patient dose estimation.