DISEASE CHARACTERISTICS: Histologically proven previously untreated (except surgically) primitive neuroectodermal tumors (including medulloblastoma, anaplastic ependymoma, ependymoblastoma, or pineoblastoma) or high-grade astrocytomas Low-grade astrocytomas or optic tract tumors that are incompletely resected and have a progressive course not amenable to further surgery may also be allowed Evaluable disease by MRI, CT scan, or CT myelography