RT-02 POTENTIAL OF PROTON BEAM THERAPY FOR THE TREATMENT OF GLIOBLASTOMA

INTRODUCTION: Recently, proton beam therapy has attracted increasing interest in the Japanese neuro-oncological field because of the insurance approval for pediatric brain tumor, chordoma, and chondrosarcoma. We have developed the high dose radiotherapeutic strategy using proton beam for malignant glioma in our institution since long before. Here we retrospectively analyzed the efficacy of this treatment strategy. METHODS: Thirty-four patients with newly diagnosed GBM who underwent high dose proton beam therapy 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). Concurrent chemotherapy consisted of ACNU in the early 6 cases or TMZ in the late 28 cases. The survival outcome and adverse events were analyzed. RESULTS: The median overall survival time and progression free survival time for all 34 patients were 35.7 months (95%CI, 28.1–43.4) and 11.2 months (95%CI, 6.8–15.7), respectively. No significant survival difference according to the chemotherapy regimen was shown. Failure patterns after proton beam therapy include 19 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. As for adverse events, symptomatic radiation necrosis was observed in 9 cases. The median time to onset of necrosis after radiation was 18.2 months (95%CI, 10.2–26.2). There were 8 cases of long survivors over 5 years out of 34 cases (23.5%). Of these, 6 cases developed symptomatic radiation necrosis. CONCLUSIONS: Our results indicate that high dose proton beam therapy of 96.6Gy (RBE) prolonged survival in selected GBM patients. With appropriate patient selection and potent treatment for radiation necrosis, high dose proton beam therapy has a great potential to improve survival in GBM patients.