Stereotactic Radiosurgery for WHO Grade 2 and 3 Oligodendroglioma: An International Multicenter Study

Abstract

INTRODUCTION: Oligodendrogliomas are primary brain tumors classified as IDH-mutant and 1p19q co-deleted in the 2021 WHO Classification. Surgery, fractionated radiotherapy and chemotherapy are well established treatments for these tumors, but there are few studies evaluating the efficacy of stereotactic radiosurgery (SRS). As these tumors are less infiltrative than astrocytomas and typically recur locally, they could be appropriate for local therapy such as SRS. METHODS: This was a retrospective multicenter study performed through the International Radiosurgery Research Foundation (IRRF). Adult patients were included if they underwent single-fraction SRS for a grade 2 or 3 oligodendroglioma. The primary endpoints were overall survival and progression-free survival. Secondary endpoints included clinical evolution and occurrence of adverse radiation events or other complications. RESULTS: Eight institutions submitted data for a total of 55 patients with a median clinical follow-up of 24 months. Median age at treatment was 46 years old and median pre-treatment KPS was 90. Median treatment volume was 4cc and median marginal dose delivered was 15Gy. The KPS remained stable post-SRS in 51% and worsened in 46.7% of patients, most often due to tumor progression (73.1%). Radiation-induced changes occurred in 29.6% of which 4 patients were symptomatic. Median progression-free survival was 17 months, with actuarial rates of 60.1% at 1 year, 31% at 2 years and 24.4% at 5 years after SRS. Median overall survival post-SRS was 58 months, with actuarial rates of 91.5% at 1 year, 83.4% at 2 years and 49.3% at 5 years post-SRS. Factors significantly associated with worsened survival were WHO grade 3 and prior radiotherapy and chemotherapy. Factors significantly associated with worsened PFS were WHO grade 3, prior radiotherapy and chemotherapy and higher treatment marginal dose. CONCLUSIONS: SRS appears to be a valuable management option for oligodendrogliomas.