Stereotactic MRI-guided Adaptive Radiation Therapy for Non-metastatic Pancreatic Cancer; Outcomes and Toxicity Analysis for Patients Treated in an Underserved Urban Center

Background: Stereotactic MRI-guided Adaptive Radiation Therapy (SMART) is an emerging technology for treatment of pancreatic cancer patients. Initial results show favorable survival and toxicity. However, data is still sparse overall, and especially in underserved patient populations. The purpose of this study is to review SMART outcomes at our underserved urban academic cancer. Objectives: Stereotactic MRI-guided Adaptive Radiation Therapy (SMART) is an emerging technology for treatment of pancreatic cancer patients. Initial results show favorable survival and toxicity. However, data is still sparse overall, and especially in underserved patient populations. The purpose of this study is to review SMART outcomes at our underserved urban academic cancer. Methods: In this IRB approved retrospective chart review we reviewed 98 patients with non-metastatic pancreatic cancer, who completed SMART between November 2018-January 2021. All 98 patients were treated with 50 Gy in 5 daily fractions with adaptive technique as deemed appropriate by treating radiation oncologist. The primary endpoints were overall survival (OS), progression free survival (PFS), and both acute and late grade 3+ GI toxicity. OS, PFS, locoregional control and distant control were estimated by Kaplan-Meier method and compared using log-rank test. The effect of clinical features on OS was assessed using univariate and multivariate Cox proportional hazard models. OS and PFS were calculated from completion of radiation. Grade 3+ GI toxicity probably or definitively related to radiation was recorded. All incidences of GI bleeding, regardless of attribution, were also recorded. Results: Median follow up was 20.9 months from time of diagnosis and 14 months from radiation. 21 (21%) patients were borderline resectable, 42 (43%) locally advanced, 22 (22%) medically inoperable and 13 (13%) resectable. Neoadjuvant chemotherapy was given to 86 (88%) patients with a median of 3.5 months of chemotherapy (range 1-12), leaving 11 (12%) patients who did not have systemic chemotherapy. Median overall survival from radiation for the whole group was 15.7 months, and 1-year OS was 58%. There was a statistically significant worsening of overall survival from diagnosis between ECOG 2+ and ECOG 0/1 patients (HR 1.94, 1.05-3.57). 27 (27%) patients went on to have surgical resection with 23 (82%) having R0 resection, and 3 (11%) have an R1 resection. Improved OS was seen in patients with surgical resection (HR 0.06, 0.02-0.23). Acute grade 3+ GI toxicity from radiation was seen in 4 (4%) patients and late toxicity from radiation was seen in 6 (6%) patients. GI bleeding was seen in 16(16%) patients, 10 (62%) of which were on anticoagulation at the time of GI bleed and 5 (19%) of which had surgery. Portal vein complications occurred with 7 (7%) having portal vein thrombosis and 6 (6%) portal vein stenosis. Conclusions: SMART showed durable responses in pancreatic cancer patients with an acceptable toxicity profile. Attention needs to be paid to the moderate incident of GI bleeding, however further work is necessary to determine if bleeding was due to radiation, surgery, or disease progression. Surgical resection as well as performance status of ECOG 0-1 were associated with improved overall survival. Further follow up will be necessary to determine further durability of treatment response and long-term survival in these patients