Safety and Efficacy of MR-Guided Re-Irradiation in Patients with GI Malignancies

Abstract

<h3>Purpose/Objective(s)</h3> This study aimed to assess the safety of administering re-irradiation in the abdomen or pelvis with MR-guided radiation therapy to patients with primary gastrointestinal (GI) malignancies. <h3>Materials/Methods</h3> A retrospective analysis was performed on a total of 9 patients that received MR-guided re-irradiation from March 2018 to February 2022 at a single institution. Patients were re-irradiated with 5 fractions using a dose constraint to re-irradiated mucosal structures of V 20 Gy <1cc. Treatment and clinical parameters including staging, histology, prescription radiation dose, and time interval between radiation treatments were collected. Patients were monitored for acute and late toxicity. <h3>Results</h3> Majority of the patients had pancreatic adenocarcinoma (n=6; 66%) and localized disease (n=6; 66%). The median age at the time of re-irradiation was 58 years (range 36-84 years) and median follow-up was 16 months (range 0.4- 39 months). 8 patients had surgery following the first dose of radiation. The median time between radiation treatments was 11.6 months (range 6.8 -87.9 months). The mean prescription was slightly higher at the time of re-irradiation compared to the initial prescription dose). The mean total prescription was 158.0 Gy EQD2 equivalent dose (range 99.4 Gy – 200 Gy). Majority of the patients experienced no acute toxicity or grade 1 toxicity, including fatigue and abdominal pain. One patient experienced grade 2 abdominal cramping. Dose constraints were met in all patients. No patients had recurrence in the re-irradiated field. Two patients experienced additional recurrences in their initially radiated fields after re-irradiation. No patients experienced late toxicity. <h3>Conclusion</h3> MR-guided re-irradiation in patients with GI malignancies may be a safe alternative in select patients. Further studies are needed to optimize patient selection and safe dose constraints.