Background: Upper abdominal / lower back pain characterizes celiac plexus involvement from pancreatic and other cancers which may impair HRQOL; its satisfactory treatment is an unmet clinical need. We hypothesized that ablative radiation delivered to the celiac plexus would decrease pain and improve HRQOL. Methods: An international single arm Phase II study included patients with an average pain level ≥ 5/11 on the brief pain inventory (BPI), ECOG 0-2, and anatomical involvement of the celiac axis. The intervention was a single fraction of 25Gy delivered to the celiac plexus. The primary endpoint was ‘complete or partial (≥2 points) pain response’ based upon the BPI ‘average pain’ 11-point scale. Changes in Health-related QOL at 3 & 6 weeks compared to baseline were secondary endpoints as measured by FACT-Hep, > 8 point change being the minimal clinically important difference (MCID). Evaluable patients included eligible irradiated subjects, who had stable pain levels pre-treatment, and were alive 3 weeks’ post-treatment. The sample size was 90 evaluable patients, giving 90% power to show response rate ≥ 40%. Opioid usage was assessed using intravenous morphine equivalent dose. Sensitivity HRQOL analyses imputed worsened outcomes (-9 for total FACT-Hep) for missing data. Results: Between 2018 and 2022, 149 patients were enrolled, 90/125 who received treatment were evaluable. Median age was 65.5 years (range 28-88), 65% were female, 92% had pancreatic cancer, and 86% had metastatic disease. Median Zubrod PS was 1, median number of systemic treatment lines was 1 (range 0-5), and median baseline opioid use 31 mg/d. At 3 weeks, 48 (53.3%, 95% CI 42.5-63.9) had at least a partial pain, the BPI ‘average pain’ score decreased by a mean of 2.5 points at 3 weeks (86/90 reported) and 3.2 points at 6 weeks (67/90 reported), both p < 0.001. Opioid usage decreased by 0.6 mg/d at 3 weeks (NS) and 16.9 mg/d at 6 weeks (p = 0.005). The FACT-Hep total score increased by 7.8 points at 3 weeks (54/90 reported, NS diff. from 8) and 16.6 points at 6 weeks (45/90 reported, sig. > 8, p = 0.01), showing an improvement in patients’ HRQOL. Changes in FACT-Hep were especially noted in the Physical Well Being subscale. The Trial Outcome Index (sum of physical, functional & disease-specific concerns) increased markedly at 3 weeks (6.6 points, p = 0.005) after treatment and even more after 6 weeks (14.5 points, p < 0.). Sensitivity analyses demonstrated improvements in HRQOL at 3 and 6 weeks (1.1, 3.8), but these were less than MCID. Conclusions: Celiac plexus SBRT decreases pain and opioid use amongst patients with pancreatic cancer and other tumors invading the celiac axis. The treatment appears to improve HRQOL. Supported by Gateway for Cancer Research and the Israel Cancer Association. Clinical trial information: NCT03323489.