Abstract ID: 111 Monte Carlo modeling of Orthovoltage treatment fields

Computational power and anthropomorphous phantoms advances in the last years have extended greatly the number of potential applications of Monte Carlo methods in the medical field. Aiming at an orthovoltage treatment plan definition, the results of Monte Carlo simulations performed with the MCNP6 code on two different typologies of computational models have been compared: Unstructured Mesh (UM) model and Voxel model. The capability to simulate the particle transport directly on the unstructured mesh model geometry has been recently introduced in the release 6 of MCNP [1] , which has been chosen for this study. These kind of models overcome the insurgence of voxel effects [2] and provide a more accurate description of volumes and complex surfaces. The simulations were performed on anthropomorphous models based on anonymous CT scans. Firstly, the UM model was obtained from the CT scans thanks to the SCAN-IP mesh tools (Simpleware), and secondly the CT was voxelized with different voxel sizes in order to compare and gauge the voxel effects. The radiation source simulates the Orthovoltage X-Ray tube in use at IRCCS-ASMN in Reggio Emilia, tested in different configurations and tube voltages. The computational source has been validated with experimental measures on the real one applied on heterogeneous slab phantoms. The validation showed good agreement of the simulated setups with the experiments, with deviations varying accordingly to the source configuration, but always below 5–6%. The comparison between the two models showed how, with decreasing voxel sizes, the voxel models results partially converge to the UM models values. Furthermore, it was highlighted that the major deviations between the models resulted where the dose gradient is higher, along the field borders and when tissue heterogeneity is more and more considered. The study shows how the UM model can be implemented for evaluating the dose deposition within anthropomorphous phantoms and, in perspective, be used in treatment planning.