Chemotherapy, Radiation Therapy, and Peripheral Stem Cell Transplantation in Treating Children With Newly Diagnosed Medulloblastoma or Supratentorial Primitive Neuroectodermal Tumor

OBJECTIVES: * Estimate the response rate to topotecan in children with newly diagnosed medulloblastoma or supratentorial primitive neuroectodermal tumors who have measurable residual disease after surgery. (Topotecan window closed to accrual 9/10/2001) * Determine the feasibility of four courses of high-dose chemotherapy (vincristine, cisplatin, and cyclophosphamide) with peripheral blood stem cell support after craniospinal irradiation (CSI) in these patients. * Estimate the 5-year overall survival and progression-free survival in patients treated with risk-adapted CSI and high-dose chemotherapy. * Compare changes in intellectual functioning in patients treated with reduced-dose vs standard-dose CSI. * Estimate the incidence of ototoxicity associated with risk-adapted CSI and posterior fossa boost(s) given by 3-D conformal radiotherapy technique combined with amifostine and cisplatin. OUTLINE: This is a multicenter study. Patients are assigned to 1 of 2 treatment groups based on risk status. * Group 1 (average-risk): Patients receive filgrastim (G-CSF) subcutaneously (SC) or IV daily until peripheral blood stem cells (PBSC) are harvested. PBSC are harvested when blood counts recover. Patients then receive craniospinal irradiation (CSI) 5 days a week for 6 weeks. Beginning 6 weeks after completion of CSI, patients receive high-dose chemotherapy comprising vincristine IV followed by cisplatin IV over 6 hours on day -4 and cyclophosphamide IV over 1 hour on days -3 and -2. Patients receive amifostine IV over 1 minute a maximum of 5 minutes prior to cisplatin infusion and then 3 hours into cisplatin infusion. PBSC are reinfused on day 0. Patients receive G-CSF SC beginning on day 1 and continuing for a minimum of 7 days or until blood counts recover. Vincristine IV is administered on day 6. G-CSF is stopped 48 hours prior to beginning subsequent courses of chemotherapy. High-dose chemotherapy repeats every 4 weeks for 4 courses. * Group 2 (high-risk): Patients receive topotecan IV over 4 hours on days 1-5 and G-CSF SC or IV beginning 24 hours after completion of the first course of topotecan and continuing until PBSC are harvested. Treatment repeats every 3 weeks for 2 courses. If an adequate number of PBSC are not harvested, the patient undergoes a second harvest of PBSC after the second course of topotecan. Patients then receive CSI, high-dose chemotherapy, amifostine, and PBSC support as in group 1. (Topotecan window closed to accrual 9/10/2001) Patients undergo neuropsychological testing prior to radiotherapy and chemotherapy and then at 1, 2, and 5 years. Patients are followed at 1, 2, 4, 6, 9, 12, 15, 18, and 24 months and then every 6 months for 3 years. PROJECTED ACCRUAL: A total of 12-36 patients will be accrued for this study within 5 years.