Combination Chemotherapy Followed by Peripheral Stem Cell Transplantation or Bone Marrow Transplantation in Treating Patients With Brain Cancer

DISEASE CHARACTERISTICS: Diagnosis of one of the following malignant brain tumors: Anaplastic astrocytoma Glioblastoma multiforme Anaplastic oligodendroglioma Medulloblastoma High-grade ependymoma Germ cell tumors Pineoblastoma Other primitive neuroectodermal tumors Recurrent disease or resistant to conventional therapy (e.g., surgery, radiotherapy, or standard chemotherapy) No prior myeloablative doses of thiotepa OR Newly diagnosed malignant glioma with minimal residual disease after prior radiotherapy Minimal residual disease is defined as tumor with maximum diameter of less than 1.5 cm by MRI and no corticosteroid dependency PATIENT CHARACTERISTICS: Age: Over 1 to under 50 Performance status: Karnofsky 70-100% OR Lansky 70-100% Life expectancy: More than 12 weeks Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 10 g/dL (transfusion allowed) Hepatic: Bilirubin less than 1.5 times upper limit of normal (ULN) SGOT/SGPT less than 2.5 times ULN Alkaline phosphatase less than 2.5 times ULN Renal: Creatinine less than 1.5 times ULN Creatinine clearance at least 70 mL/min BUN less than 1.5 times ULN Cardiovascular: Ejection fraction greater than 50% OR Shortening fraction greater than 27% No evidence of myocardial ischemia on EKG if over 40 years of age Other: HIV negative No AIDS-related illness No frequent vomiting or medical condition that would preclude oral medication (e.g., partial bowel obstruction) No other malignancy within the past 2 years except surgically cured carcinoma in situ of the cervix or basal cell or squamous cell skin cancer Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: At least 2 weeks since prior biologic therapy or immunotherapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered Endocrine therapy: See Disease Characteristics Radiotherapy: See Disease Characteristics At least 6 weeks since prior radiotherapy and recovered At least 6 weeks since prior brachytherapy or radiosurgery Surgery: See Disease Characteristics Recovered from prior major surgery