RADT-04. OPTIMAL CLINICOGENETIC CRITERIA FOR POSTOPERATIVE RE-IRRADIATION IN RECURRENT GLIOBLASTOMA: KROG 21-02

Abstract Patients with glioblastoma (GBM) often have disease progression after standard temozolomide-based chemoradiation. The benefits and optimal use of re-irradiation (re-RT) following re-operation (re-OP) in recurrent glioblastoma (rGBM) remain uncertain. In this study, we assessed the efficacy and safety of postoperative re-RT in patients with isocitrate dehydrogenase-wild-type rGBM, aiming to identify survival benefits and determine clinicogenetic criteria for patient selection. Data from the Korean Radiation Oncology Group 21-02 retrospective study were evaluated, including 531 patients with rGBM from 2013 to 2019. A subset of 164 patients undergoing re-OP was analyzed for survival and benefits of postoperative re-RT. Additionally, 206 patients receiving re-RT, irrespective of re-OP, were evaluated for risks of radiation necrosis. The overall survival (OS) after re-OP was the primary endpoint. Statistical analyses included the Kaplan–Meier method and log-rank test for OS, Cox proportional hazards regression model for univariate and multivariate analyses, and the Fine–Gray competing risk model for assessing the risk of brain necrosis. The median OS after re-OP was 13.4 months. Kaplan–Meier analysis revealed significantly better OS for those receiving re-RT (17.6 months) than for those who did not (11.0 months; p=0.002). Factors associated with improved OS included higher Karnofsky Performance Status scores, postoperative re-RT, and additional systemic therapy post-re-OP. Factors associated with adverse outcomes included recurrence outside the initial RT field and homozygous deletion of CDKN2A/B. The incidence of grade 2 or higher RT necrosis was 5.8% among those undergoing both re-OP and postoperative re-RT. Postoperative re-RT appears to be associated with enhanced survival and minimal toxicity in patients with rGBM following temozolomide chemoradiation. Our study suggests a novel clinicogenetic criterion for re-RT after re-OP in rGBM, which requires further validation.