Use of Radiotherapy by High-energy Protons in the Postoperative Treatment of Brain Tumor

Abstract

Fractionated irradiation using 250 mega electron volt protons alone or in combination with ⁶⁰cobalt (Co) gamma ray was given postoperatively to 8 patients with glioma and 2 patients with meningioma. A single field was used for all patients. The irradiated field varied from 28 to 144 cm²; the irradiated depth was from 6 to 11 cm and the width of the Bragg peak was from 5 to 10 cm in the proton radiotherapy. Dose aim was approximately 74.5 Grey (Gy) over 46 days in the proton alone radiotherapy and was approximately 84.8 Gy over 56 days in the combined therapy with ⁶⁰Co gamma ray. The dose increment was from 2.5 to 5.0 Gy per fraction as treatment progressed in the proton radiotherapy. No evident increased intracranial pressure developed. Nine patients were given the planned dose of irradiation. One patient with glioblastoma multiforme deteriorated during the treatment and the planned course was not completed. The patient was reoperated. Another patient with glioblastoma multiforme deteriorated 1 month after planned irradiation of 84.2 Gy and was diagnosed as having a regrowth of the tumor. Evident and viable tumor cells were observed in the outline of the center of tumor tissue in the irradiated field. Furthermore no evident radiation effect developed in the peritumoral area showing low density on computerized tomography. Exudative dermatitis with much epilation was seen at the proton beam entrance site in all patients with complete radiotherapy. Seizure was also seen in 6 out of 9 patients. Two patients with grade III or II astrocytoma and 2 patients with meningioma were in good health 6 to 9 months after radiotherapy, but the other patients with glioblastoma multiforme died or deteriorated 1 to 5 months after radiotherapy. The issue of proton radiotherapy for brain tumor was discussed. In conclusion, it is necessary to investigate further the optimal dose and dose distribution in the tumor tissue, irradiation technique, and the combined therapy with some drug in the treatment of malignant glioma.