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Multistage Monte Carlo Treatment Simulation Framework for Hitachi ProBeat-V Intensity Modulated Proton Primary and Micro-Beam System

V Moskvin

V Moskvin*, A Pourmoghaddas , F Pirlepesov , W Yao , J Farr , St. Jude Children's Research Hospital, Memphis, TN


SU-H2-GePD-T-2 (Sunday, July 30, 2017) 3:30 PM - 4:00 PM Room: Therapy ePoster Lounge

Purpose: To commission the primary (spot sigma ~2.5 mm at 221 MeV) and micro-beams (spot sigma of 1.4 mm) proton therapy system and design an independent dose calculation engine for intensity modulated proton treatments.

Methods: A proton therapy system (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat-V) with modifications to produce microbeams was simulated based on design information provided by the vendor using the TOPAS 2 Monte Carlo code. Convergent and divergent beam models were applied. The Monte Carlo model was validated with the commissioning measurements of lateral spot profiles in air and integrated depth doses (IDDs) in water. The computational framework utilizes TOPAS 2 and FLUKA Monte Carlo code for treatment simulation.

Results: The model of the convergent beam with a focus at the isocenter produces the best description of the micro-beam spot. The primary beam may be simulated using a divergent beam model. The computed spot sizes (sigma) agree with microDiamond detector (PTW) measurements for micro-beam and Lynx (IBA) and film for primary beam option within 0.1 mm. The measured integrated depth doses (IDDs) are within statistical error of simulation (less than 1.3%). Therapeutic ranges (R90) are within 0.15 mm across all energies for both beam types. The MC generated data were used for the commissioning of the radiotherapy planning system (RTPS) (Varian Medical Systems, Eclipse v13.7.15). Patient simulation continues from the phase space files computed based on the patient plan information within TOPAS 2 framework or FLUKA Monte Carlo code.

Conclusion: The micro-beam and primary beam proton therapy system computational model was implemented in the TOPAS coupled with FLUKA framework. The simulation of the microbeam requires usage of convergent beam model. Monte Carlo based dose computation framework will be helpful for treatment plan verification with new micro-beam modality and primary beam, and for research purposes including radiation biology.

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