31. RADIATION NECROSIS IN STEREOTACTIC RADIOSURGERY AND CHECKPOINTS INHIBITORS FOR BRAIN METASTASES FROM LUNG ADENOCARCINOMA

PURPOSE: Treatment with stereotactic radiosurgery (SRS) and immune checkpoint inhibitors (ICI) is increasingly common for brain metastases (BM) from lung adenocarcinoma. Rates of radiation necrosis (RN) with SRS in the setting of ICIs is an ongoing area of research. We investigated rates of RN in patients with BM from lung adenocarcinoma treated with SRS with or without concurrent ICIs. METHODS: We identified 39 patients at a single institution who underwent SRS treatment for BM from lung adenocarcinoma. Of these, 19 (49%) received SRS without ICIs and 20 (51%) patients received ICIs within a month of SRS. The rate of RN, defined by MRI features and histology when available, was compared between each group using multivariate analysis. Kaplan Meier survival estimates were calculated based on overall survival and compared to median survival predicted by the graded prognostic assessment. RESULTS: Overall survival for all patients from diagnosis of brain metastases was 16.6 months (range 3.6–45.9) and median survival predicted by the graded prognostic assessment was 13.7 months (range 6.9–26.5). In total 11 (28%) patients developed MRI and/or histologic evidence for RN during the follow-up period; 5 of 20 (25%) from the SRS with ICI group and 6 of 19 (31%) from the SRS without ICI group. In multivariate analysis, ICI treatment had no significant impact on rates of RN between groups (OR 0.72 [95% CI: 0.17–2.93]; p=0.65) while bevacizumab treatment was associated with a decreased RN risk (OR 0.88 [95% CI: 0.43–0.99]; p=0.02). CONCLUSION: Retrospective analysis of patients with BM from lung adenocarcinoma treated with SRS suggested that administration of ICIs does not increase risk for development of RN. Further, concomitant treatment with bevacizumab may decrease risk of RN. These findings suggest that patients with BM from lung adenocarcinoma can be treated with combination therapy without increased risk of neurologic toxicity.