Room: Stars at Night Ballroom 1
Purpose: To demonstrate the feasibility of using an FDA-cleared treatment planning system (TPS) to perform pencil beam scanning (PBS) proton therapy treatment planning with a dynamic collimation system (DCS). Modeling a DCS is a unique treatment planning challenge due to its capability to move four independent nickel trimmers in synchrony with the proton beam as opposed to a conventional collimator which maintains a constant configuration for each energy layer.
Methods: The Astroid Proton Treatment Planning Application is an FDA-cleared TPS that is capable of dose computation and treatment plan optimization for PBS. To account for the dosimetric effect of the DCS, all four independent trimmers were incorporated into the Astroid calculation geometry. Five patients that were previously treated for brain tumors using PBS and planned in the Eclipse TPS were selected and re-planned in Astroid. The same beam models used for those patients were included in Astroid. Integration of dynamically collimated distributions from a DCS was achieved for a representative plan and compared to its respective uncollimated PBS plan. The same prescription dose and beam angles used in the clinical plans were used in the Astroid plans. The spot and trimmer positions in a DCS plan were determined by an external algorithm and imported into Astroid for spot weight optimization based on dose-volume objectives. Plans were evaluated according to relevant physical comparison metrics.
Results: Astroid produced uncollimated PBS plans of the same quality as the clinical plans as well as DCS plans with an 11.4% reduction in mean dose to the 10 mm surrounding the PTV while maintaining appropriate target coverage.
Conclusion: It is feasible to use an FDA-cleared TPS to perform treatment planning for the DCS with minor modifications. Further dosimetric studies and measurement will be performed to validate the accuracy of such treatment plans.
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.