DISEASE CHARACTERISTICS: Histopathologically confirmed supratentorial glioblastoma multiforme or gliosarcoma Diagnosis by surgical biopsy or resection required The following tumor types are specifically excluded: Astrocytoma with atypical or anaplastic features Well differentiated astrocytomas Tumors originating in the brain stem Tumors located within 10 mm of the optic chiasm Infratentorial tumors Multifocal malignant glioma Recurrent malignant glioma Well circumscribed contrast-enhancing tumor on pre- and postoperative contrast-enhanced CT or MRI with a maximum diameter (in any direction) of 40 mm required Tumors that do not enhance on postoperative CT or MRI excluded Concurrent enrollment on RTOG-9308 encouraged