Combination Chemotherapy Plus Radiation Therapy in Treating Adult Patients With Brain Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed central nervous system cancer including: * Medulloblastoma with either local residual disease of greater than 1 cm\^2 on MRI following resection or evidence of metastases (M1-4) * Other primitive neuroectodermal tumors * Ependymoma with evidence of subarachnoid metastases * Must have less than 1 cm of midline shift or no acute elevated intercranial pressure PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * ECOG 0-2 Life expectancy: * Not specified Hematopoietic: * WBC greater than 4,000/mm\^3 * Platelet count greater than 125,000/mm\^3 * Hemoglobin greater than 10 g/dL * No preexisting hematologic condition that would increase toxicity or limit ability to comply with evaluations and follow-up Hepatic: * Bilirubin less than 2 times upper limit of normal (ULN) * SGOT less than 2 times ULN * Alkaline phosphatase less than 2 times ULN * No preexisting hepatic condition that would increase toxicity or limit ability to comply with evaluations and follow-up Renal: * Creatinine greater than 70 mL/min * No preexisting renal condition that would increase toxicity or limit ability to comply with evaluations and follow-up Pulmonary: * No history of significant pulmonary disease or, if there is preexisting pulmonary disease, then DLCO greater than 60% of predicted * No preexisting pulmonary condition that would increase toxicity or limit ability to comply with evaluations and follow-up Other: * No…