DISEASE CHARACTERISTICS: Glioblastoma multiforme (GBM) or brain stem tumor following surgery (if feasible) and local radiotherapy, as follows: Pathologically confirmed primary GBM Gliosarcomas and multifocal GBM eligible Unbiopsied diffuse intrinsic pontine tumors Nonenhancing with gadolinium on MRI T1 hypodense and T2 hyperdense No recurrent or progressing disease following radiotherapy No leptomeningeal dissemination by radiographic evaluation including head MRI and either whole-spine MRI with gadolinium or myelogram Positive CSF cytology alone allowed No extraneural metastases