Survival outcomes and toxicity of stereotactic MR guided adaptive radiation therapy (SMART) in locally advanced pancreatic cancer.

Abstract

787 Background: NRG GI 011, a study randomizing patients with locally advanced pancreatic cancer (LAPC) with and without ablative radiation therapy, has strict entry criteria regarding performance status, induction chemotherapy, and CA 19-9 to best select patients who may benefit from ablative radiation. This study evaluates the effect of those patient characteristics on survival outcomes of patients with LAPC treated with stereotactic MR guided adaptive radiation therapy (SMART) at a single urban medical center. Methods: A retrospective review was conducted of 106 LAPC patients treated with SMART between 2018 and 2024. All patients received SMART with 50Gy in 5 fractions, with or without induction chemotherapy. Overall survival (OS) was measured from diagnosis and from the end of RT and estimated using Kaplan-Meier (KM) analysis, and KM curves were compared using log-rank tests. Multivariate Cox proportional hazards models tested the impact of performance status (PS), largest tumor size at diagnosis (TS), induction chemotherapy (yes vs no), carbohydrate 19-9 (CA19-9), and age on survival outcomes. Acute and late grade ≥3 toxicities were graded per CTCAE v5.0. Results: The median OS from diagnosis was 16.5 months (95% CI: 15.1-18.0), and 9.1 months from the end of RT (95% CI: 7.7-10.4). In univariate analysis, lower CA19-9, younger age, and a PS of 0-1 with induction chemotherapy was significantly associated with improved OS from diagnosis (p < 0.05) while tumor size was not. Multivariate analysis confirmed lower CA19-9 and PS 0-1 with induction chemotherapy were independent predictors for improved OS from diagnosis. The 38 patients who meet the NRG GI 011 enrollment criteria had a median OS of 25.1 months and a 3-year survival of 35.2%. For OS from the end of RT, only PS 0-1 with induction chemotherapy remained significant for improved OS (p = 0.058) in the multivariate model. Grade ≥3 acute toxicities occurred in 2.8% of patients and grade ≥3 late toxicities occurred in 13.2% of patients. Conclusions: SMART for LAPC demonstrates excellent OS from both diagnosis and from the end of RT with low rates of grade ≥3 acute and late toxicities. Elevated CA19-9, worse PS, and lack of induction chemotherapy emerged as key negative prognostic factors in treating LAPC with SMART, confirming the enrollment criteria for NRG GI 011.