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Modeling and Validation of the a New Proton Therapy System Using a Monte-Carlo Environment Optimized for Protons

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K Grantham

K Grantham1*, E Klein2 , (1) University of Missouri, Columbia, MO, (2) Washington University, Saint Louis, MO


SU-E-T-546 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Monte-Carlo modeling is an important tool for understanding the behavior of therapeutic proton beams in a heterogeneous media such as the patient. To gain confidence that a Monte-Carlo model is accurate in complex geometries and media, it must first be compared with measurement in simple situations. This study documents the validation of our Monte-Carlo Model.

Methods: A model of the MEVION s250 Proton therapy system was created in the TOPAS Monte-Carlo environment using machine geometry and field shaping system information provided by the vendor. For each of 24 options, validation of the TOPAS model was performed by comparing the dose scored by TOPAS to the dose measurements obtained during the commissioning of the treatment planning system. The measurements compared consisted of: pristine peak depth-dose profiles, in-air profiles for a standard-sized square field (20cmx20cm or 10cmx10cm depending on the maximum field size for each option) at isocenter and at 20cm upstream and downstream of isocenter, and in-air profiles with a half-beam blocked aperture at isocenter and at 20cm upstream and downstream of isocenter. For all Monte-Carlo simulations, 10^8 particle histories were run.

Results: Range measurements of the Monte-Carlo simulations matched the measured data within 1mm. Distal fall-off of the simulated fields matched within <1mm. Lateral penumbra and field size measurements of the standard-sized square and half-beam blocked fields matched within 1mm at all three planes compared. A small difference was seen in the in-air profiles at doses <20%. The suspected cause of the difference was the aperture shape. The measured data utilized a divergent aperture. The Monte-Carlo calculation used a non-divergent aperture.

Conclusion: The validation measurements indicate that we were able to accurately model the MEVION s250 Proton therapy system using Monte-Carlo Calculations. This may reduce the commissioning time for future users.

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