Dosimetric Feasibility of Flash-Compatible Single-Energy Bragg Peak (SEBP) Proton Therapy for Hypofractionated Pancreatic Cancer
Abstract
Purpose
Hypofractionated proton therapy for pancreatic cancer is limited by the proximity of radiosensitive abdominal organs. Single-energy Bragg peak (SEBP) proton delivery enables ultra-high dose-rate (UHDR) irradiation and may facilitate FLASH compatible treatments. Preclinical studies show that FLASH irradiation can spare normal tissues while maintaining tumor control, suggesting potential benefit for toxicity-limited abdominal sites. This study evaluates the dosimetric feasibility of SEBP planning for hypofractionated pancreatic radiotherapy and compares target coverage, organ at risk (OAR) doses, and dose-rate characteristics with conventional intensity-modulated proton therapy (IMPT).
Methods
This novel SEBP technique uses range shifters and range compensators and was implemented on an in-house treatment planning platform to enable conformal FLASH investigation. Three pancreatic cancer cases prescribed 55Gy in 5 fractions were planned using both IMPT and SEBP techniques with identical beam and couch angles. SEBP plans were optimized to increase per-spot dose rate by merging low monitor unit spots and reducing total spot count while maintaining plan quality. Target coverage and dose metrics were compared between techniques. Dose rate volume histograms (DRVHs) were used to quantify the fraction of OAR volume receiving UHDR (V40Gy/s).
Results
SEBP plans achieved target coverage comparable to IMPT, with CTV coverage of 98% for both techniques and maximum doses less than 120%. For SEBP, large bowel, stomach, small bowel, and spinal cord D0.5cc values slightly increased relative to IMPT but remained within institutional constraints. Combined kidney V15Gy and liver mean dose remained low for both techniques. Dose-rate analysis demonstrated that SEBP delivery achieved FLASH compatible dose-rates, with high-dose regions achieving V40Gy/s.
Conclusion
SEBP proton planning enables hypofractionated pancreatic treatments with acceptable target coverage and OAR doses while achieving FLASH compatible dose-rate characteristics. These results establish SEBP as a feasible planning approach for abdominal FLASH proton therapy and provide a foundation for future delivery and biological investigations.