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Building a Brachytherapy Parallel Monte Carlo Simulation Framework Through Source Parameterization


M Zhang

M Zhang*, W Zou, T Chen, L Kim, N Yue, Cancer Institute of New Jersey, New Brunswick, NJ

SU-E-T-514 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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.

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