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 preexisting psychiatric condition that would increase toxicity or limit ability to comply with evaluations and follow-up No prior or concurrent malignancies within the past 5 years except curatively treated carcinoma in situ of the cervix or basal cell or squamous cell skin cancer Not pregnant or nursing Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: No increasing doses of steroids for intracranial disease within 3 days of registration Radiotherapy: No prior radiotherapy Surgery: 10-28 days since prior surgical resection OR At least 5 days since prior biopsy