Beta considerations in internal dose estimation using a Monte Carlo code

Abstract

Calculations of Absorbed Fraction (AF) of radiation energy, for various source and target organs of interest in internal dosimetry, neglect the transport of electron by-products from photon interactions as well as beta radiation from radionuclide decay. Without electron and beta transport, values of AF for photon radiation are overestimated when the source organ is the target organ and underestimated for nearby target organs which do not contain radioactivity. Currently, calculating AF for electron and beta radiation has not been possible. Corrections for these inadequacies are made using the INDOSE code, developed for use with a modified version of the Electron-Gamma Shower (EGS4) code. EGS4 is a simulation code that uses the Monte Carlo method. Calculations of AF were performed for various energies of photon radiation homogeneously distributed in 10 source organs and electron radiation distributed in 6 source organs. Results from INDOSE-EGS4 code for photon radiation, without electron transport, show good agreement with published data. For identical source and target organs, AF values for photon radiation with and without electron transport, show identical results below about 0.5 MeV and an increasing difference above this energy. For electron radiation, AF decreases linearly with energy when source and target organs are identical. However, for other target organs, AF gradually increases with energy leveling off to a constant value. More accurate dose estimates are obtained from the AF values presented.