Comparative Study on Homogeneous and Inhomogeneous Photon Dose Distribution from a High Dose Rate Ir-192 Brachytherapy Source using MCNP5

aThe purpose of this study is to simulate and analyse the influence of inhomogeneities on the dose rate distribution on brachytherapy and verifying a good tool for dose calculation. The study focused on the evaluation and comparison of dose rate distribution in water phantom using Monte Carlo Code (MCNP5). A simulated High Dose Rate (HDR) 192Ir brachytherapy source was used. The dose was calculated in a homogenous water phantom at angular cells around the source. For inhomogeneties, cone cells were used to calculate dose distribution around Ir source in water and inhomogeneous medium that includes water, soft tissue, air and skeletal bone. Both the track length energy deposition tally (F6) and pulse height tally (* F8) were used in the isotropic dose calculation. The difference in calculations between the two tallies in the angular anisotropic distribution ranged from 0.0056 to 0.4213% for water and water plus soft tissue phantoms respectively. Impact of soft tissue on dose rate distributions was clear with maximum difference of 5.4%. The maximum differences due to inhomogeneities were 8.157% and 14.779% for F6 and for * F8 respectively. The results indicated that tally F6 is a good tool to calculate the effect of inhomogeneity due to soft tissue, air and bone on brachytherapy in an inhomogeneous medium.