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Determination of Compensator and Patient Scattered Factors Using Monte Carlo Simulation Techniques for Passively Scattered Proton Beams

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M Prusator

M Prusator*, S Ahmad , Y Chen , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


SU-I-GPD-T-183 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To utilize Monte Carlo simulation technique to calculate compensator scatter factors (CSF) and patient scatter factors (PSF) and to compare these factors to the corresponding factors calculated by the Eclipse treatment planning system (TPS) and measured in an anthropomorphic phantom for the Mevion S250 proton therapy system.

Methods: PSF and CSF measurements were made with an anthropomorphic phantom representing a brain treatment field. TLD detectors were placed in the phantom to acquire dose for the field, and to calculate PSF. Using identical treatment parameters, TLD dose measurements were made in a water phantom with and without compensator in place to calculate CSF. The TOPAS (TOolkit for PArticle Simulation) Monte Carlo code and Eclipse TPS was used to calculate PSF and CSF factors for the same anthropomorphic phantom. The measurements were used to benchmark our Monte Carlo code for further use. Utilizing the same technique, PSF and CSF factors were also calculated using simulation and TPS for a patient brain case.

Results: For the anthropomorphic phantom case, the CSF calculated by Monte Carlo, measured in phantom and calculated in TPS all agreed to within 0.2%. The measured PSF differed from Monte Carlo and TPS calculated factors by 0.7% and 5.2%, respectively. With regards to the patient brain case, CSF agreed between the TPS and Monte Carlo to within 0.4% and simulated PSF was 4% higher than what was predicted by the TPS.

Conclusion: Monte Carlo simulation is a viable option to calculate PSF and CSF factors. The excellent agreement between the measured and simulated PSF and CSF in the phantom thus shows that our simulation model is reliable. The discrepancy between measured and TPS calculated PSF factor in the phantom indicates that there may possibly be errors in TPS method of calculating PSF factor which is currently being investigated.

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