3379 - Safe Delivery of Ablative, Non-Adaptive Pancreas and Elective Nodal RT in Borderline Resectable and Locally Advanced Pancreatic Cancer
Presenter(s)
R. Abou Zeidane1, D. Bajor2, A. Mahipal2, M. Conces2, M. Lumish2, A. Mohamed2, S. Chakrabarti2, J. Hardacre3, J. Winter3, J. Ammori3, R. Kashani1, E. A. Wiegner1, J. A. Dorth1, A. T. Price1, and L. E. Henke1; 1Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, 2Department of Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, 3Department of Surgery, Division of Surgical Oncology, University Hospitals Seidman Cancer Center, Cleveland, OH
Purpose/Objective(s): Radiation therapy (RT) is often used neoadjuvantly or definitively in borderline resectable (BR) and locally advanced pancreatic cancer (LAPC). In both scenarios, expanded target volumes that incorporate elective nodal irradiation (ENI) are now recommended. However, ENI combined with ablative RT dosing may increase risk, especially when online adaptive RT (ART) is unavailable, or in approaches that prioritize target coverage over critical organ-at-risk (OAR) sparing. Here we report the safety and oncologic outcomes of using a non-adaptive, planning organ-at-risk volume (PRV) approach to deliver ablative, 5-15fx RT with ENI to patients (pts) with BR/LAPC.
Materials/Methods: This cohort study included all adult pts with BR or LAPC who received ablative RT on an institutional prospective pancreas RT registry between January 2023 and July 2024. Pts received 50Gy/5fx (50/5) or 67.5 Gy/15fx (67.5/15; for OAR invasion or infeasible fiducial placement) to the primary tumor and ENI volume (defined as a 7mm peri-celiac and SMA expansion) with a 5mm PTV expansion. RT was planned and delivered at exhale breath-hold, using active breathing control. Strict constraints of V33Gy <0.5cc and V36Gy <0.5cc were applied to the stomach, duodenum, small and large bowel and to 5mm PRVs expanded from them, respectively. A planning PTV_Opt structure (PTV – [PRVs + additional 5mm gradient margin]) was used to escalate dose to 50 or 67.5Gy, with minimum 50%Rx PTV coverage required. Outcomes including overall survival (OS from diagnosis), freedom from local progression and distant metastasis-free survival (FFLP and DMFS from end of RT), and acute (<90 days) or late RT-related GI toxicity were analyzed using descriptive statistics and Kaplan-Meier analyses.
Results: 54 pts with BRPC (46.3%) and LAPC (53.7%) were identified, with mean age at diagnosis of 69.6 (± 12.2) yrs. 46 pts received chemotherapy prior to RT and 9 pts (16.7%) were medically ineligible. 47 pts completed 50/5 and 7 pts received 67.5/15. 18 pts underwent surgery after RT (33.3%). At a median follow-up of 19.9mo, CTCAE v 5.0 Gr3 or higher acute and late RT-related GI toxicity were 0% and 7.4% (4 Gr3 ulcers in 54 evaluable pts). Median OS was 18.5mo overall. Estimated 12 and 18mo OS rates were 76% and 48.4% for BRPC and 82.5% and 52.9% for LAPC (p 0.99). Estimated 18mo FFLP was 65% overall; 67.7% for BRPC vs. 62.2% for LAPC (p 0.45). DMFS at 6mo was 54.8% and was 65.8% in resected vs. 45.5% unresected pts (p 0.14).
Conclusion: Ablative, 5-15fx pancreas RT in combination with ENI can be safely delivered without online ART, with observed toxicity rates similar to historic evaluations of SBRT without ENI and/or without ablative dosing. Despite target coverage sacrifice through strict PRV constraint use and 16.7% of pts receiving no chemotherapy, median OS outcomes compared favorably to LAP07 and A020510 benchmark trials and to other reports of ablative RT dosing. For institutions without access to ART, our approach offers a safe means for ablative RT with ENI for BR/LAPC.