Application of GATE/Geant4 for internal dosimetry using male ICRP reference voxel phantom by specific absorbed fractions calculations for photon irradiation

Abstract

Targeted internal radiation is a type of radiation therapy in nuclear medicine (NM) that is efficient in small and disseminated tumours specially in metastatic disease. In any medical procedure that involves radiation exposure the radiation dosimetry is required and the dose distribution in NM is of great interest to estimate absorbed doses in organs of risk and tumours. Specific absorbed fraction (SAF) is an essential parameter that connects the dose received by a tissue and the emitting volume and, currently, SAF calculations using Monte Carlo (MC) simulations may be considered one of the most appropriate methods for individualized dosimetry. In this work, SAF values for International Commission on Radiological Protection adult male voxelized phantom were calculated using GATE/Geant4 Standard and Livermore packages and compared with MCNPX and EGSnrc reference data. Photon irradiations with energies ranging from 10 keV to 10 MeV were simulated in three different source organs: liver, lungs and thyroid. SAF values of four target organs (breasts, lungs, colon wall and stomach wall) were calculated and compared with reference data. Obtained results agreed with the reference data with an average accuracy better than 3% for energies above 50 keV and up to 3.3% for the full range of energies. Results suggest that, although good agreement was found for both GATE/Geant4 packages with MCNPX and EGSnrc, Livermore package shows more stability and it is slightly more accurate than Standard package, mostly when its results are compared with EGSnrc. However, the agreement of both GATE/Geant4 packages with the MCNPX and EGSnrc codes might depend on the pair TO/SO. Finally, results indicate that GATE might be used for internal dosimetry of gamma emitters and also encourage the development of a GATE SAF database using reference phantoms.