Geant4/GATE Monte Carlo Code for Internal Dosimetry Using Voxelized Phantom

It is of great interest to estimate absorbed doses in organs before radiation therapy, especially in nuclear medicine field. In this regard, the internal dose distribution is required. According to the MIRD formalism, Specific Absorbed Fraction (SAF) is an essential parameter for internal dosimetry. In the present work, SAF values for the voxelized phantom (Golem) of the GSF-National Research Center for Environment and Health were calculated using Geant4/GATE with Standard packages and compared with GSF Monte Carlo reference data. Photon irradiations of 30, 100 keV and 1 MeV energy were simulated in eleven different sources and target organs: liver, kidneys, lungs, brain, pancreas, spleen, colon, Red bone marrow (RBM), stomach, thyroid and adrenals. The SAF for self-absorption and for cross-irradiation to other organs were calculated and compared with literature. The results agree with published data, with an average relative difference less than 3%, for the self-absorption of 100 keV and 1 MeV photon energies. The agreement of Geant4/GATE and GSF code might depend on the distance between target and source, the target mass and the photons energy. Generally, the present results indicate that GATE might be used with gamma emitters for internal dosimetry in regard to our prospective works.