Current Advances in Proton FLASH Radiotherapy in Abdominal Cancers.

Proton FLASH radiotherapy represents a promising innovation in the treatment of abdominal cancers, offering the potential to expand the therapeutic window by delivering ultra-high dose rates (UHDR) that spare normal tissue while maintaining tumor control. This approach is particularly beneficial for gastrointestinal (GI) tumors, where radiation dose escalation is often limited by the radiosensitivity of nearby organs. This review explores recent preclinical, planning, and technical developments in proton FLASH for abdominal sites and outlines the challenges and future directions for clinical translation. We reviewed the available published literature on proton FLASH radiotherapy, with a focus on abdominal applications. Recent preclinical studies in abdominal models have shown encouraging, though inconsistent, evidence of reduced toxicity with proton FLASH. Parallel advances in treatment planning have also demonstrated technical feasibility in achieving UHDR across complex abdominal geometries. However, key challenges remain, including variability in biological responses, lack of standardized dose-rate definitions, delivery system constraints, and the absence of robust clinical data. Although only limited clinical trials are currently underway, proton FLASH may enable safer hypofractionation, reirradiation, and dose escalation strategies in the future. Its successful clinical translation will require coordinated advances in biology, physics, and technology, supported by rigorous preclinical validation and carefully designed clinical trials.