RT-4 Treatment outcome of proton beam therapy for glioblastoma

Introduction: Proton beam therapy enables high dose irradiation for tumors while reducing the dose to surrounding normal tissue due to the sharp energy peak called the Bragg peak. We retrospectively analyzed the efficacy of the high dose radiotherapeutic strategy using proton beam for glioblastoma (GBM) in our institution. Methods: Twenty-nine patients with newly diagnosed GBM who underwent high dose proton beam therapy concomitant with temozolomide were investigated. All patients received hyperfractionated concomitant radiotherapy consisting of X-ray radiotherapy (50.4Gy in 28 fractions) and proton beam therapy (46.2Gy [RBE] in 28 fractions). The survival outcome and adverse events were analyzed. Results: The median overall survival time and progression free survival time for all 29 patients were 31.0 months (95%CI, 25.9–36.1) and 11.0 months (95%CI, 7.8–14.2), respectively. No significant survival difference according to the MGMT methylation status was shown. Failure patterns after proton beam therapy included 17 cases of local recurrence, 3 cases of distant recurrence, and 5 cases of dissemination. Although there was no significant difference in time to recurrence according to the failure pattern, there was a tendency of longer survival in the local recurrence group. Regarding adverse events, radiation necrosis was observed in 8 cases (including 2 asymptomatic cases). The median time to onset of necrosis after radiation was 18.2 months (95%CI, 10.3–26.2). There were 5 cases of long survivor over 5 years out of 29 cases (17.2%). Of these, 4 cases developed radiation necrosis. Conclusions: Our results indicate that high dose proton beam therapy of 96.6Gy (RBE) prolonged survival in selected GBM patients. Particularly in long survivors, special attention and effective treatment to radiation necrosis is a remaining problem.