DISEASE CHARACTERISTICS: Histologically confirmed malignant glioma determined from prior stereotactic biopsy or cytoreductive surgery for removal of a supratentorial brain tumor Unilateral supratentorial tumor, measuring at least 1 cm, as determined by CT scan or MRI No more than 1 focus of tumor and no tumor crossing the midline Surgical treatment indicated at baseline evaluation Received prior definitive (greater than 5,000 cGy) external beam radiotherapy more than 3 months ago Evidence of progression At time of tumor resection and Gliadel wafers implantation: Intraoperative pathological diagnosis on frozen section or squash preparation of malignant glioma OR Glioblastoma multiforme or anaplastic astrocytoma on permanent sections from a prior surgery and an intraoperative pathological diagnosis on frozen section or squash preparation of tumor, glioma, or malignant glioma (not necrosis)