Purpose: The use of energy-specific collimation and an arc-based delivery technique in pencil beam scanning (PBS) proton therapy hold significant synergistic potential. Each of these technologies have demonstrated a unique ability to improve organ-at-risk sparing while maintaining a high degree of target coverage in PBS. The purpose of this work is to develop a novel external beam delivery approach that combines the geometric flexibility afforded by arc-based deliveries with the enhanced target conformity capabilities of energy-specific collimation.
Methods: A research-based treatment planning system was used to simulated arc-based PBS treatments delivered using a model of the IBA universal nozzle beam line and optimized using a genetic optimization framework. Collimation was incorporated using an analytical model of the dynamic collimation system (DCS), a PBS collimator capable of energy-layer specific collimation through the rapid sequencing of four trimmer blades. The uncollimated and DCS-collimated PBS arc treatments were planned on a chordoma patient data set with an intracranial target and compared against a standard multi-field approach.
Results: Combining collimation with an arc-based delivery approach achieved the highest target conformity and dose sparing of surrounding healthy tissue among all the approaches evaluated. Compared to an uncollimated multi-field and arc delivery, the median dose was reduced by 17.9% and 11.4%, respectively, to the adjacent 10 mm of healthy tissue surrounding the PTV with the addition of dynamic collimation. Utilizing an arc delivery with the DCS also reduced the integral dose to the whole healthy brain tissue by 1.7% and the maximum skin dose by 55.4% relative to the collimated, multi-field approach.
Conclusion: The results from this work are promising. Combining arc therapy with energy-specific collimation further improves plan conformity and healthy tissue sparing beyond either of these techniques alone. It is expected that utilizing such techniques will improve the delivery robustness and treatment efficiency.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R37CA226518. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.