Long-term efficacy of celiac plexus radiosurgery for pancreatic cancer pain: An international phase II trial.

714 Background: Celiac plexus radiosurgery demonstrates impressive short-term pain control (3-6 weeks) in pancreatic cancer patients with minimal side effects, leading to NCCN guideline inclusion. In the trial, irradiation of the adjacent tumor was left to physician's discretion, but did not impact short-term pain outcomes (the primary endpoint). In this analysis we 1) report long-term efficacy, and 2) test the hypothesis that concurrent tumor irradiation affects durability. Methods: Single-arm study of 125 patients across five countries with baseline pain ≥5/10 and pancreatic cancer or celiac axis invasion. Subjects lacking pain scores at both 3- and 6-weeks post treatment were excluded. Pain measured via Brief Pain Inventory (weeks 0-6), then Numeric Rating Scale. Linear mixed-effects models with both linear & quadratic time terms analysed pain trajectories. Sensitivity analyses for missing data included multiple imputation, 'last observation carried forward', and worst-case scenarios. Prescription dose was tested as a moderator variable in the mixed-effect model. Results: A total of 107 patients analyzed (median age 64, 54% female, 92% pancreatic cancer, 86% metastatic). Median baseline pain was 6/10 (SD 1.7). Of the 82 cases in which the adjacent tumour was included within target volume, it was prescribed a median dose of 15Gy. Patients alive at 12/26/39 weeks: 79/33/24; pain outcome available for: 52/25/16. Median survival was 18 weeks. Peak effectiveness was at 18.5 weeks (95% CI: 15.7-20.7) with 3.4-point reduction (60% improvement, p<0.001), followed by gradual waning. Multiple imputation suggested sustained efficacy through 39 weeks. Higher prescription doses to adjacent tumor were associated with improved palliative durability (dose×time² interaction: p=0.046). Conclusions: Celiac plexus radiosurgery provides clinically meaningful pain reduction for at least four months. A post-hoc hypothesis generating analysis revealed concurrent tumor irradiation enhanced durability with a dose-response relationship. These exploratory, potentially practise changing findings warrant validation in a randomized trial. Financial support: Gateway for Cancer Research , Israel Cancer Association . Clinical trial information: NCT03323489 .