SU-E-T-514: Building a Brachytherapy Parallel Monte Carlo Simulation Framework Through Source Parameterization

Abstract

Purpose: This work aimed to parameterize a brachytherapy source phase space file by using multiple probability density functions. Based on this, we built a brachytherapy parallel Monte Carlo (MC) simulation framework with simple geometry input, light memory consumption, accurate dose calculation, and fast speed. Methods: A Varian VariSource HDR brachytherapy source (Ir‐192) was generated in Geant4. A phase space file with 7 indexes for each particle (3 positions, 3 directions, 1 energy) was scored at the source surface. A parameterization was performed on the phase space file with the following assumptions: (1) A particle's energy is independent of its position and direction; (2) Particle locations in the transverse plane (x‐y) are uniform; (3) A particle's direction depends on its position along the source axis (z). Parameterization accuracy was evaluated by comparing radial dose function and anisotropic function as defined in TG‐43 between the phase space file‐represented source (S_phase) and the parameterized source (S_para). A brachytherapy MC framework was designed by parallel computing the dose contributions from individual dwell positions using the parameterized source. Results: The phase space file was successfully parameterized. Compared to the 2 GB phase space file, the parameterized source input was 300 kB without sacrificing computation speed. The radial dose function difference between S_phase and S_para was at most 2%. The anisotropic function agreed well between the two sources. The largest difference of about 5% was only observed within 10 degrees of the source axis. This difference has no significant impact on clinical applications. Conclusion: A method is developed to parameterize the source phase space file for MC brachytherapy dose calculation at almost no expense of accuracy. With much less memory consumption, using a parameterized source allows parallel computing for clinical implementation of brachytherapy MC dose calculation.