Monte Carlo calculation of photon specific absorbed fractions in digimouse voxelized phantom using InterDosi code

Development of new radiopharmaceuticals is carried out on a small animal such as a mouse. With the aim to well-assess internal absorbed dose reaching various organs of a mouse, physical quantities defined by MIRD methodology known as specific absorbed fractions (SAFs) were evaluated using a voxelized mouse phantom. In our study, in order to provide more accurate photon SAFs, we used recent chemical compositions and densities of human organs taken from ICRP publication number 110. A new computational Geant4-based code called InterDosi has been developed to calculate SAFs for source-target organ pairs in Digimouse phantom irradiated by discrete monoenergetic photons of energies ranging from 0.015 to 4 MeV. Results show that, photon self-irradiation SAFs decrease with increasing energy or mass. For a cross-irradiation case, the photon SAFs were found to depend on distance source-to-target and organs close to the source have the most important photon SAFs. A comparison between our results and those reported in an earlier study with similar values of voxel sizes, masses, densities and chemical compositions, generally shows a significant agreement between them. Therefore, for a given configuration (energy, source), a smooth variation was found in the case of a self-irradiation. Contrariwise, medium discrepancy (less than 24%) was found in the case of a cross-irradiation, which can be attributed to the strong impact of the implementation of physics of the simulation in the two different codes and also the large statistical uncertainties associated to the calculation of SAFs in distant organs. •InterDosi Geant4-based code has been developed to calculate SAFs in Digimouse phantom.•SAFs have been calculated for discrete monoenergetic photons of energies ranging from 0.015 to 4 MeV.•Self-irradiation SAFs decrease with increasing energy or mass.•Cross-irradiation SAFs depend on distance source-to-target and they are important for organs that are close to the source.