Carbon Ion Beam Reirradiation in Recurrent High-Grade Glioma

BACKGROUND: Patients with recurrent glioma after prior radiotherapy have a poor prognosis. Carbon ion beam radiotherapy offers highly conformal dose distributions and more complex biological radiation effects eventually resulting in optimized normal tissue sparing and improved outcome. The aim of this study was to analyze toxicity, local control and overall survival after reirradiation of recurrent high-grade glioma with carbon ion radiotherapy. METHODS: Between 10/2015 and 12/2018, 30 patients (median age: 59 years) with recurrent high-grade glioma were reirradiated with carbon ion beams and retrospectively analyzed. Diagnosis of recurrent glioma was based on magnetic resonance imaging. Thirteen patients had repeated resection prior to reirradiation and 24 patients underwent additional chemotherapy. The median initial radiation dose was 60 Gy and the median time interval between the initial and repeated radiotherapy was 10 months. The reirradiation dose was 45 Gy (relative biological effectiveness) applied in 15 fractions. All patients received regular follow-up imaging after reirradiation. Kaplan-Meier estimation, log rank test and Cox regression analysis were used for statistical assessment. RESULTS: Applying common toxicity criteria, there were no grade 5 or 4 adverse events, while 8 patients showed grade 3 adverse events. The median follow-up after reirradiation was 11 months and the median overall survival after diagnosis of recurrent high-grade glioma was 13 months. The 6-, 12- and 24-month overall survival rates after diagnosis of recurrent high-grade glioma were 76%, 50% and 19%, respectively. Upon multivariate Cox regression analysis, a Ki67 score of the initial tumor histology of less than 20% was prognostic. Repeated resection or chemotherapy for the recurrent disease did not result in significantly prolonged survival. CONCLUSION: Carbon ion reirradiation in recurrent high-grade glioma is safe and feasible. No radiation-associated grade 4 toxicities were documented and treatment was tolerated well.