Validation and clinical implementation of a full Monte Carlo code for scanned proton pencil beams
(2017) PTCOG
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- Abstract
- Purpose: To present a methodology for commissioning and validating a full Monte Carlo (MC) code (TOPAS/Geant4) for proton pencil beams utilizing a double Gaussian phase space source model and a simplified range shifter implementation. Application of this source model onto an independent fast MC code (MCsquare), and comparison between MC simulations with analytical treatment planning system (TPS) are investigated. Methods: The phase space parameters and protons per MU were extracted and tuned without simulating any components of the nozzle by comparing TOPAS simulations with a series of commissioning measurements. The beam model was validated by comprehensive measurements of single spots, field size factors (FSF) and three dimensional dose distributions of Spread Out Bragg Peaks (SOBPs) both without and with range shifter. To demonstrate the application, this source model was directly implemented into a fast, dedicated PBS MC code, MCsquare. Clinical treatment cases were compared between TOPAS, MCsquare and our commercial treatment planning system. Results: Based on comprehensive comparison with measurements, TOPAS was validated for all aspects. The difference in field size factors and absolute output at various depths of SOBPs between measurement and simulation were within 2%, indicating an accurate source modeling with and without a range shifter. Comparison of two dimensional dose distributions and DVHs for representative liver case and lung case between MC and analytical calculations (TPS) highlights limitations in the TPS dose calculation in situations of highly heterogeneous geometries. Conclusions: We have proposed a universal method to model a proton PBS dedicated nozzle, with better addressing the halo inherent from nozzle and simplified implementation of a range shifter, using acceptance and commissioning measurements. We compared patient treatments between two MC codes and analytical calculations to show this tool can be implemented clinically to provide an independent dose calculation algorithm for patient specific QA and for benchmarking other dose calculation engines under development.
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Sheng Huang, Minglei Kang, Souris, K., Liyong Lin, & et al. (2017). Validation and clinical implementation of a full Monte Carlo code for scanned proton pencil beams. PTCOG. https://hdl.handle.net/2078.5/225517