Study of Proton Therapy in Adjuvant Pancreatic Cancer

The investigators hypothesize that resected pancreatic cancer patients will benefit from enhanced local control with the addition of radiation therapy to adjuvant FFX. The recently reported PRODIGE 24 study, demonstrated that 12 cycles of adjuvant FFX without radiation therapy significantly improved survival and time to metastatic failure rates as compared to GEM alone. Excessive distant failures rates using prior adjuvant systemic therapies, may have limited the impact of radiation therapy; therefore, improvements in systemic control can increase the benefit of local control. In this study, the investigators utilize 5 fraction PRT, delivered over 1 week, during adjuvant FFX (between cycles 6 and 7) to minimize the interruptions in chemotherapy as well as to reduce the length of time from surgical resection to initiating adjuvant radiation therapy. Conventional radiation therapy is typically delivered over 5 weeks and is commonly given after the completion of adjuvant chemotherapy. Conventional radiation therapy cannot be given concurrently with FFX due to the synergistic toxicities. In contrast, PRT significantly reduces the exposure of normal tissues to the effects of radiation therapy and has been safely delivered using a 5 fraction schedule with chemotherapy, as previously discussed. Chemotherapy will consist of mFOLFIRINOX in 14-day cycles x 12 as used in the PRODIGE 24 study: * Irinotecan 150 mg/m2 IV day 1 * Oxaliplatin 85 mg/m2 IV day 1 * Leucovorin 400 mg/m2 IV day 1 * 5-fluorouracil 2,400 mg/m2 IV days 1-3 (no bolus) * Pegfilgrastim 6 mg SC on-body injector day 3 (optional, up to investigator's discretion, can alternatively do day 4 without on-body injector) * Suggested supportive care medications: fosaprepitant 150 mg IV day 1, dexamethasone 12 mg IV day 1, ondansetron 16 mg IV day 1, dexamethasone 4 mg PO q AM days 2-3, ondansetron 8 mg PO BID days 2-3. * Dose adjustments will be permitted at the discretion of the treating oncologist based on patients' prior tolerability to FFX * Proton radiation will consistent of 5 daily doses of 5 GyE total, ideally administered Monday through Friday but can be administered within 7 business days, between cycles 6 and 7