WE‐E‐108‐05: Evaluation of the XRAD 225Cx MC Source Model in Heterogeneous Mediums

Purpose: This study was performed to benchmark a Monte Carlo source model of the XRAD 225Cx irradiator under heterogeneous conditions. Methods: The BEAM/EGS was used to model 225 kV photon beams from a small animal irradiator (Precision XRAD225Cx). Benchmarking the model in heterogeneous media was performed in a heterogeneous phantom (4×4×4 cm3) composed of solid water and cortical bone. The 10 mm field size virtual source from BEAMnrc was used to compute the 3D dose distribution in DOSXYZnrc. Benchmarking the simulation against measurements was performed using EBT2 film. Heterogeneous conditions were further validated using the phase space file for the 20 mm field size. Gamma analysis was performed to further validate the beam model for the heterogeneous configuration phantom. Results: The MC simulation indicates that there is a 2.4 times increased dose deposition in cortical bone, in agreement with published data. This increased dose deposition, however, was not observed in film measurements and it is investigated further. Gamma analysis was performed for 20 mm field size applicator and the Result of the analysis for a confined region. The single beam with 20 mm diameter circular field irradiation demonstrates a good agreement within the region of interest, with 94% of the calculated data meeting the 5%/0.5 mm criterion. Conclusion: Our kV Monte Carlo source model demonstrates excellent agreement with measurement in heterogeneous conditions.