DISEASE CHARACTERISTICS: Recurrent brain tumor based on one of the following: Tissue diagnosis if there was a prior diagnosis of astrocytoma or oligodendroglioma or if there is a question of radiation necrosis from prior interstitial brachytherapy Metabolic activity in excess of normal cortex measured by 18-fluorodeoxyglucose uptake on PET One of the following histologic types required: Glioblastoma multiforme Anaplastic astrocytoma Anaplastic oligodendroglioma Anaplastic mixed glioma Tumor progression required, i.e.: 28% increase in contrast-enhancing area or 50% increase in contrast- enhancing volume over at least 4 weeks Measurable disease required No history, surgical findings, or radiographic signs of intratumoral hemorrhage