Program Information
Validation and Clinical Implementation of a Full Monte Carlo Code for Scanned Proton Pencil Beams
S Huang1*, M Kang1 , K Souris2 , C Ainsley1 , T Solberg3 , J McDonough1 , C Simone4 , L Lin1 , (1) University of Pennsylvania, Philadelphia, PA, (2) Universite Catholique de Louvain, Woluwe-saint-lambert, Bruxelles, (3) UCSF Comprehensive Cancer Center, San Francisco, CA, (4) University of Maryland, Baltimore, MD
Presentations
TU-H-CAMPUS-TT-5 (Tuesday, August 1, 2017) 4:30 PM - 5:30 PM Room: Therapy ePoster Theater
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 comparisons between MC simulations and 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 through comprehensive measurements of single spots, field size factors (FSFs) 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 comparisons 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 accurate source modeling with and without a range shifter. Comparison of two dimensional dose distributions and DVHs for representative cases between MC and analytical calculations (TPS) highlights limitations in the TPS dose calculation in situations of highly heterogeneous geometry.
Conclusion: We have proposed a novel method to model proton PBS dedicated nozzle, better addressing the halo inherent from the 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.
Funding Support, Disclosures, and Conflict of Interest: This research was funded, in part, by a Varian industry grant and a Department of Defense grant under contract agreements DAMD17-W81XWH-07-2-0121 and W81XWH-09-2-0174. Kevin Souris is supported by a research grant from IBA s.a..
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