DISEASE CHARACTERISTICS: Histologically confirmed malignant glioma - Recurrent glioblastoma - Anaplastic astrocytoma - Mixed anaplastic glioma For recurrent glioblastoma: Required documented progression must include an increase in tumor size of at least 25% or appearance of new lesion For anaplastic astrocytoma or mixed anaplastic glioma: Must have measurable, contrast enhancing disease on postoperative CT or MRI scan No postoperative radiation or chemotherapy If patients have received prior brachytherapy or stereotactic radiosurgery, they must have confirmation of true progressive disease rather than radiation necrosis by PET scanning or biopsy