Survival outcomes following stereotactic MR guided adaptive radiation therapy (SMART) in medically inoperable pancreatic cancer.

Abstract

786 Background: There is ongoing interest in randomized studies utilizing stereotactic MR guided adaptive radiation therapy (SMART) in patients with medically inoperable pancreatic cancer. This study evaluates overall survival (OS) from diagnosis and from the end of radiation treatment (RT) of patients with medically inoperable pancreatic cancer. Methods: A retrospective review analyzed medically inoperable pancreatic cancer patients treated with 50 Gy in 5 fractions of SBRT at a single urban medical center. OS was calculated from diagnosis and end of RT to the date of death or last follow-up. Kaplan-Meier estimates and 95% confidence intervals (CI) were reported, and the Kaplan-Meier curves were compared using log rank tests. Cox’s proportional hazard model was used to determine the combined impact of Zubrod performance status (PS) (0-1 vs. 2-3) and tumor size (TS) at diagnosis (<2.35 cm or ≥2.35 cm) with OS (diagnosis) and OS (RT). Multivariate models were adjusted for age at diagnosis and induction chemotherapy (yes vs no). Hazard ratio (HR) and 95% CI were reported. Acute (<=90 days) and late grade ≥3 toxicities were graded per CTCAE v5.0. Results: 62 patients were included; the median OS was 10.4 (95% CI: 7.3-13.5) months from diagnosis. The receipt of induction chemotherapy was the only independent predictor of OS from diagnosis; 16 months from diagnosis compared to 8.8 months for no induction group (p = 0.021). TS was the only independent significant predictor for OS from RT. Patients with PS 2-3 and TS ≥2.35 cm showed the worst OS from diagnosis and end of RT compared to patients with PS of 0-1 and TS <2.35 cm (Table 1). Late Grade 3 upper GI bleeding occurred in one patient (1.85%) and acute Grade 3 abdominal pain or diarrhea occurred in two other patients (3.7%). Conclusions: Medically inoperable pancreatic cancer patients treated with induction chemotherapy and SMART have favorable survival outcomes. Delivery of SMART to patients with poor performance status and large tumor size may not be impactful. These findings support the importance of patient selection in medically inoperable pancreatic cancer patients receiving SMART. OS from diagnosis and RT versus PS+TS. Variable OS from diagnosis (months) OS from end of RT (months) PS of 0-1 and TS <2.35 cm Median = 11.9 Median = 10.4 PS 2-3 and TS ≥2.35 cm Median = 8.7 HR = 2.1 Median = 5.4 HR = 2.4 * *p<0.05.