2953 - Single Institution Treatment Outcomes for Patients Treated with SBRT for Borderline Resectable Pancreatic Cancer

L. I. Banla¹, D. D. Shi², Y. H. Chen³, M. Rosenthal⁴, J. E. Leeman⁵, R. van Dams², N. E. Martin², M. Lam², B. Wolpin⁶, J. D. Mancias², M. Fairweather⁷, G. Molina⁷, J. Wang⁷, T. Clancy⁷, H. Singh⁶, S. Moningi², and H. J. Mamon²; ¹Harvard Radiation Oncology Program, Boston, MA, ²Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, ³Department of Data Science, Dana-Farber Cancer Institute, Boston, MA, ⁴Department of Radiology, Brigham and Womens Hospital/Dana-Farber Cancer Institute, Boston, MA, ⁵Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, ⁶Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, ⁷Department of Surgery, Brigham and Womens Hospital / Dana-Farber Cancer Institute, Boston, MA

Purpose/Objective(s): Surgery remains the only curative option for pancreatic cancer, but few patients have resectable disease at diagnosis. Most present with borderline resectable pancreatic cancer (BRPC) or unresectable tumors. The treatment goal for BRPC is to reduce the local disease burden to enable resection. The choice of the appropriate neoadjuvant therapy to reach this goal is controversial but often includes a combination of chemotherapy, conventional radiation therapy, or stereotactic body radiation therapy (SBRT). This study reports the outcomes of patients with BRPC who are treated with neoadjuvant SBRT. Materials/

Methods: We conducted a retrospective study of consecutive patients treated with SBRT for a diagnosis of BRPC categorized according to NCCN criteria. Patients were treated at a single institution from April 2015 through July 2020. The primary outcome was completion of surgical resection and the association between this outcome and patient factors or neoadjuvant treatment details was investigated via logistic regression. Surgical outcomes such as R0 resection rate were recorded, as well as oncologic outcomes including survival and disease progression.
Results: Our analysis included 57 patients with a follow-up of 16.5 months following diagnosis. Most patients (50/57) had tumors located in the head/uncinate process. The mean tumor size was 3.1cm. Vascular involvement was limited to one vessel in 26 patients, two vessels in 27 patients, and three vessels in 4 patients. Before SBRT, all patients received neoadjuvant chemotherapy (median of 8 chemotherapy cycles). Most (48/57) received FOLFIRINOX or gemcitabine/nab-paclitaxel (7/57). The median SBRT dose was 36Gy. The median overall survival from the time of diagnosis was 18.0 months (95% confidence interval (95CI): 15.2-21.2), and the median progression-free survival was 11.9 months (95CI: 11.0-14.0). Of the 57 patients, 29 completed surgical resection (26 R0 resections), while 28 patients did not complete surgery due to advanced or metastatic disease. On both univariable (odds ratio (OR) 5.54, P = 0.006) and multivariable (OR 7.58, P = 0.005) analyses, a cumulative radiation dose of 36Gy or higher was associated with the completion of surgical resection. Other factors including age, gender, performance status, tumor location, neoadjuvant chemotherapy regimen, tumor size, and number of involved vessels did not have an association with the completion of surgical resection.
Conclusion: In this single-institution study of BRPC patients treated with SBRT, approximately half of the cohort reached the goal of surgical resection, most of which were R0 resections. Of the patient factors and treatment parameters evaluated, elevated cumulative radiation dose was the only factor associated with the completion of surgical resection. These data contribute to the evolving discussion on the most effective approaches to the management of BRPC.