Favorable Survival after Definitive Ablative RT in Surgically Resectable Pancreatic Cancer Patients

Abstract

Surgical resection has been considered the only curative option for patients with pancreatic adenocarcinoma (PDAC). Ablative RT ≥100Gy BED10 (A-RT) is associated with favorable survival in patients with locally advanced unresectable disease. We sought to evaluate A-RT outcomes in patients with technically resectable disease who did not undergo surgery. Our prospectively maintained database of patients treated with A-RT was queried for consecutive patients with radiographic T1/T2 resectable PDAC. Patients were treated with a standardized technique within a large academic cancer center regional network. Ablative RT using several hypofractionated regimens was delivered on either standard Linacs with respiratory motion management, CBCT image guidance and selective adaptive replanning or MR-Linac with compression belt and daily on-line adaptive replanning. Freedom from local progression (FFLP), distant metastasis-free and overall survival (DMFS and OS, respectively) were analyzed using the Kaplan Meier estimates. Between 2016 and 2022, 28 patients (54% male) with radiographically resectable PDAC received definitive A-RT. Median age was 80 (interquartile range, 77-84) years and 23 (82.1%) had KPS of 80 or below. Eighteen patients (64.3%) had T2 cancer, 5 (17.9%) were node positive, and 23 (82.1%) had head location. Median size was 2.6 (range, 1.6-4.0) cm with a median carbohydrate antigen 19-9 (CA19-9) of 160.5 (0-1823) U/mL. Twenty patients (71.4%) received induction chemotherapy for a median of 2.4 (0-6.2) months. RT regimens delivered on conventional Linacs unless otherwise indicated included 75Gy in 25 fractions (n = 15), 67.5Gy in 15 fractions (n = 10), 50Gy in 5 (N = 2, MR Linac), 60Gy in 10 (n = 1). 24-month FFLP and DMFS were 78.8% (52.3-91.7%) and 17.7% (95% CI, 5.8%-34.8%), respectively. 24-month and 48-month rate of OS from A-RT were 49.1% (95% CI, 27.53-67.5%) and 36.3 (95%16.0-57.1%). Grade 3 acute and late GI toxicity was noted in 3 and 1 patients, respectively, including 2 bleeding events treated with transfusions. There were no ≥ grade 4 events. In patients with surgically resectable PDAC we found that definitive A-RT following multiagent induction therapy was associated with oncologic outcomes similar to resection with minimal toxicity.