Definitive SBRT in unresectable pancreatic cancer: Long-term outcomes with moderate vs high dose approaches.

677 Background: Locally advanced pancreatic cancer (LAPC) represents a substantial clinical challenge. Chemotherapy (CT) remains the backbone of therapy; consolidation radiotherapy (RT) is often used to enhance local control. Stereotactic body RT (SBRT) has attracted increasing interest due to its ability to deliver high RT doses to the tumor while minimizing dose to organs at risk and associated lymphopenia. Prior studies of dose escalation have reported mixed results. Methods: This analysis of a prospectively maintained single-institution database included 206 LAPC patients treated with definitive intent, using a range of SBRT doses between 2008-24. Biologic effective dose (BED) was calculated as follows: BED = nd * (1 + d/α:β), where n = # of doses, d = dose per fraction; α:β was set at 10. Results: Median age at diagnosis was 70 years; 50.5% of patients were women, and median KPS was 80. 171 patients received CT before SBRT, most commonly FOLFIRINOX or gemcitabine/nab-paclitaxel. Median overall survival (OS) in patients receiving CT was 17.5 (95% CI 16 -19) vs 7.8 months (mos) without CT (95% CI6.5-9.1), p