SBRT re-irradiation after prior SBRT in pancreatic cancer—outcomes and a focus on stomach and bowel toxicity

Abstract

Stereotactic body radiotherapy (SBRT) is increasingly used for pancreatic cancer; however, there is a dearth of data guiding its use after prior SBRT. We conducted an institutional review board (IRB)–approved retrospective study of patients treated with SBRT for pancreatic cancer on two occasions from 2005 to 2018. Patients were followed for response to treatment and toxicity assessment (Common Terminology Criteria for Adverse Events [CTCAE] version 5). Demographic and survival data for the cohort were described using frequencies, medians, and ranges. Survival analysis was performed using the Kaplan-Meier method. Twenty-four patients met the inclusion criteria. Local control at 1 year after the second SBRT treatment was 77.2%. Median survival from 1st SBRT course and 2nd SBRT course was 31 months and 13 months, respectively. Most patients were treated with 24 Gy in 3 fractions for their first course and 25 Gy in 5 fractions for their second course. Thirteen patients did not undergo surgery, and 9 had detailed radiation treatment planning data available with non-distorted GI anatomy. For the total summation dose (first and second courses of SBRT combined), the D0.03cc and D1cc to the duodenum received up to 46.1 Gy and 42.3 Gy, respectively, while the stomach received up to D0.03cc of 49.2 Gy and D1cc of 43.8 Gy. SBRT after prior SBRT for pancreatic cancer is a reasonably safe and efficacious treatment that leads to durable local control and reasonable survival. Retreatment of the duodenum and stomach with a D0.03cc and D1cc of at least 40 Gy may be safe, although more data is needed.