410 Background: Outcomes remain poor for those diagnosed with unresectable pancreatic cancer. SBRT and IRE have independently demonstrated high rates of local control and minimal toxicity for patients with locally advanced pancreatic cancer (LAPC). Data is limited regarding safety and efficacy in the sequential use of both therapies. Materials and Methods: A single institution retrospective matched cohort analysis was performed for patients with non-metastatic pancreatic cancer treated with induction chemotherapy and SBRT followed by IRE, compared with patients of the same cohort who did not receive IRE. Patients were paired based on age, tumor stage, GTV D95, CA19-9 prior to SBRT, and chemotherapy type to mitigate selection bias in surgical candidates. Overall survival (OS), progression free survival (PFS), freedom from local failure (FFLF) and freedom from distant failure (FFDF) were the primary outcomes compared via Kaplan-Meier survival analysis with log-rank methods. Results: From July, 2014 to February, 2020 17 patients received SBRT followed by IRE. These patients were matched with 17 patients who received SBRT from January, 2012 to March, 2019. Most patients received neoadjuvant FOLFIRINOX (82.4%) and were AJCC 8 stage III (79.4%). Median age of the overall cohort was 65.5 years and 50% were male. Median dose delivered to 95% of gross tumor volume was 32.61 Gy, and median pre SBRT CA19-9 value was 70.5 U/mL. There were no statistically significant differences in matched characteristics between the two cohorts. Among the SBRT+IRE, the median time between IRE and SBRT was 66 days (range:49-467 days). The median OS, PFS, FFLF, and FFDF for IRE+SBRT vs. SBRT alone from SBRT was 10.8 vs 15.1 months, 9.6 vs. 15.3 months, 15.7 vs. 15.3 months, 15.9 vs. 14.4 months respectively (all P > .10). 11 patients in the entire cohort experienced toxicity as a result of their radiation therapy (35%), with one G3 GIB and one patient experiencing G3 abdominal pain. Among the 17 patients who underwent IRE, nine patients experienced toxicity (53%). Most of these events were G3, with two G4 intestinal bleeds. There was zero mortality in the 90 day period post operatively. Conclusions: In a retrospective cohort,non-selective delivery ofIRE afterSBRT demonstrated no oncological benefit for patients with unresectable pancreatic adenocarcinoma compared to only SBRT. Compared to historical experiences of IRE alone, there was no increase in overall toxicity with the combination of SBRT and IRE. The optimal timing, sequencing, and indications for IRE and SBRT in LAPC remain unknown and are best assessed prospectively. [Table: see text]
How Much Was the Elective Lymph Node Region Covered in Involved-Field Radiation Therapy for Locally Advanced Pancreatic Cancer? Evaluation of Overlap Between Gross Target Volume and Celiac Artery–Superior Mesenteric Artery Lymph Node Regions
