RTHP-37. RE-IRRADIATION OF GLIOMATOSIS CEREBRI WITH WHOLE BRAIN PULSED REDUCED DOSE RATE RE-IRRADIATION

Abstract BACKGROUND Gliomatosis cerebri was removed from the 2016 WHO classification but the clinical problem of gliomatosis remains. For many of these patients, re-irradiation of the whole brain may be the only option. We have employed pulsed reduced dose rate (PRDR) radiation therapy to limit the toxicity of whole brain re-irradiation in this patient population. METHODS Consecutive patients were identified from an institutional database of patients treated with PRDR radiation to the whole brain between 2001 and 2016. Patients were treated by delivering a 20 cGy pulse of radiation every 3 minutes to opposed lateral fields with custom blocks using 6 MV photons, delivering radiation at an effective dose rate of 6.67 cGy/minute. RESULTS A total of sixteen patients were identified who underwent re-treated with WBRT. The median age was 45 (28–66) with a median KPS of 80 (range 60–100). 15 of 16 patients had high grade gliomas. The most common dose was 30 Gy in 15 fractions (range 24–41.4 Gy), giving a median total dose of 90.75 Gy (range 61.4–100.8 Gy). Median overall survival from re-irradiation was 3.8 months (range 0.1–17.0 months) and overall survival from first progression was 11.2 months. 25% of patients survived over 6 months following treatment and the overall response rate was 25% (3 PRs, 1 stable). No grade 4 or grade 5 toxicities were attributable to pulsed reduced dose rate radiation therapy. CONCLUSIONS PRDR radiation therapy provides a potential therapeutic intervention for progressive gliomatosis cerebri, providing a treatment option that can be implemented where no trial is available. As survival is short, these results will assist in counseling patients in considering re-irradiation versus supportive care.