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Validation of a Pencil Beam Model for Collimated Proton Therapy Dose Calculations

L Bennett1*, B Smith2 , D Wang1 , R Flynn1 , D Hyer1 , (1) University of Iowa, Iowa City, IA, (2) University of Wisconsin, Madison, WI,


(Sunday, 7/14/2019) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 7

Purpose: Integrating the dynamic collimation system (DCS) with a commercial treatment planning system (TPS) is a unique challenge for several reasons, the most important of which are accurately modeling the sharpened lateral penumbra and accounting for the time varying position of the trimmers in each energy layer. The purpose of this study was to validate the accuracy of uncollimated and collimated proton pencil beam spot profiles in Astroid, an FDA-cleared TPS.

Methods: All four independent nickel trimmers of the DCS were incorporated into the Astroid calculation geometry by assuming they act as infinitesimally thick square apertures. For the collimated case, the trimmers were set to two positions to represent a high degree of collimation and a moderate degree of collimation. Uncollimated and collimated integral depth dose (IDD) curves and lateral profiles of proton pencil beams were computed in a water phantom geometry and comparisons were made between calculations prepared by the Astroid TPS and those simulated using MCNP6 with an identical simulation geometry. Sufficient particle histories were ran to establish an uncertainty of less than 1% for voxels near the Bragg Peak.

Results: For a 118 MeV proton pencil beam with initial in-air sigma of 7.15 mm, the IDD curves generated from Astroid and MCNP6 were compared using a 1D gamma analysis at 1.5%/1.5mm. Greater than 97% of assessed points for the uncollimated and collimated beamlets passed the gamma criteria. The lateral profiles at two depths, the surface and the Bragg Peak, were compared using a 2D gamma analysis at 1.5%/1.5mm and total of 100% of assessed points for the uncollimated and collimated beamlets passed the gamma criteria, respectively.

Conclusion: The FDA-cleared Astroid TPS is capable of accurately modeling and calculating proton pencil beams collimated by the DCS.

Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the National Cancer Institute of the National Institutes of Health under award number R37CA226518. Hyer, Flynn, and Wang are co-inventors on a patent that has been licensed to IBA.


Protons, Radiation Therapy


TH- External Beam- Particle therapy: Proton therapy - Development (new technology and techniques)

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