Multiple-fraction-per-day external beam radiotherapy for adults with supratentorial malignant gliomas

The prognosis following therapy for adults with supratentorial malignant gliomas is poor. Standard therapy of 60 Gy of external beam radiotherapy with chemotherapy achieves a median survival time of 35 to 51 weeks following surgery. A variety of innovative therapies have been considered for therapy of malignant gliomas. Multiple-fraction-per-day (MFD) external beam radiotherapy has been evaluated by many investigators. The rationale for MFD teletherapy is based upon exploiting differences in the recovery capacity for radiation damage between slowly and rapidly proliferating tissues and/or shortening the overall treatment time. A large number of clinical trials have, for the most part, failed to show any survival benefit from MFD radiotherapy. These trials have utilized b.i.d. and t.i.d. radiotherapy with fraction sizes of 0.89 to 2 Gy to total doses of 30-81.6 Gy. The linear quadratic model of the radiation cell survival curve suggests that a biological effective tumoricidal dose > or = 10% higher than standard daily radiotherapy, with approximately isoeffective normal tissue damage, could be achieved at 1.2 Gy b.i.d. to a total dose of approximately 72 Gy. Trials of low dose per fraction MFD radiotherapy, to total doses less than 72 Gy, would be predicted to be inadequate to the task.