RADT-71. REAL-WORLD CHARACTERISTICS OF IDH-MUTANT GLIOMA PATIENTS UNDERGOING REIRRADIATION AT RECURRENCE: A MULTI-INSTITUTIONAL RETROSPECTIVE ANALYSIS

Abstract Limited data guide the treatment of IDH-mutant gliomas at post-radiation recurrence. Current clinical decisions are extrapolated from mixed molecular cohorts, resulting in inconsistent approaches, particularly for lower-grade tumors. Recurrent IDH-mutant gliomas are treated with a variety of modalities, including reirradiation, retreatment with chemotherapy, second-line systemic therapies (including the recent use of IDH inhibitors), and re-resection. Patient and treatment characteristics specific to those undergoing reirradiation remain poorly defined. We retrospectively reviewed a cohort of 558 IDH-mutant glioma patients from two academic centers, identifying 64 IDH-mutant glioma patients who received reirradiation at any point during their disease course. Histologic subtypes included WHO grades 2, 3, and 4 astrocytoma, and grades 2 and 3 oligodendroglioma. Reirradiation treatment modalities included intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery (SRS). Demographics and features, including types and dosages of radiation, extent of resection, timing of radiation for initial diagnostic surgery and subsequent therapies, and use of bevacizumab, were assessed for their impact on overall survival. At diagnosis, 10 patients received a biopsy only, 34 had a subtotal resection, and 20 had a gross total resection. Forty-nine patients received first-line radiation and were reirradiated at first progression. Of these, 12 had SRS, and 37 received IMRT. Fifteen patients delayed initial radiation in favor of observation (10) or chemotherapy alone (5), underwent initial radiation at first progression, and reirradiation at a subsequent progression. Among the cohort, 6 received more than 2 courses of radiation, and 15 were administered bevacizumab concurrently with reirradiation. Median overall survival was 96.34 months. This real-world cohort provides insight into reirradiation treatment patterns for patients with IDH-mutant glioma. Variations in radiation timing, prior treatment exposures, and histologic subtypes underscore the need for a structured framework to guide reirradiation, and a rationale for prospective studies evaluating reirradiation as a treatment strategy for recurrent IDH-mutant gliomas.