RADT-30. PROTON THERAPY FOR RE-IRRADIATION OF RECURRENT GLIOMA

Abstract

Abstract BACKGROUND Proton therapy may improve the side effect profile of re-irradiation for recurrent glioma by limiting the overlap with previous radiation dose received by the brain. Limited data exist regarding the outcomes or side effects after proton re-irradiation. METHODS We retrospectively reviewed the charts of 43 consecutive adult patients with glioma treated with uniform scanning or pencil beam scanning proton re-irradiation from June 2014-June 2022. Outcomes were estimated utilizing Kaplan-Meier analysis. RESULTS Median age of the cohort was 45 years (range 19-74). Initial histologic diagnosis was glioblastoma for 18 (42%), astrocytoma for 16 (37%), oligodendroglioma for 8 (19%) and diffuse glioma NOS for 1 (2%) patient. The median initial prescription dose was 60 Gy (range 54-61.2 Gy) with 86% receiving concurrent temozolomide. The median interval between initial radiation therapy (RT) and re-irradiation was 51 months (range 6-185 months). The median re-irradiation dose delivered was 37.5 cobalt gray equivalent (CGE) in 15 fractions (range 6-50.4 CGE in 2-28 fractions) with 34 patients receiving this dose fractionation. Concurrent systemic therapy included bevacizumab (8), chemotherapy (5), immunotherapy (2) or none (28). Overall, 40 (93%) finished the planned course and three stopped early given progression. Median survival was 11.5 months for the full cohort (95% confidence interval: 6.8-13.6 months). For patients with glioblastoma, median survival was 6.4 months (95%CI 5.0-13.5 months). For patients without glioblastoma, median survival was 11.6 months (95%CI 9.2-34.3 months). Twelve patients (28%) developed symptomatic pseudoprogression/radiation necrosis, with ten requiring increased steroids and four requiring bevacizumab. CONCLUSIONS Proton re-irradiation was well tolerated in patients with recurrent glioma, with 6.4 and 11.6 month median survival estimates for glioblastoma and non-glioblastoma histologies, respectively. Symptomatic pseudoprogression/radiation necrosis was common. Further study is needed to determine whether proton re-irradiation has improved tolerability compared to photons.