Intrathecal Radioimmunotherapy, Radiation Therapy, and Chemotherapy After Surgery in Treating Patients With Medulloblastoma

RATIONALE: Radioimmunotherapy uses radiolabeled monoclonal antibodies to locate tumor cells and deliver radioactive tumor-killing substances to them without harming normal cells. Radiation therapy uses high-energy x-rays to damage tumor cells. Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining intrathecal radioimmunotherapy and radiation therapy with combination chemotherapy may kill any tumor cells remaining after surgery. PURPOSE: Phase II trial to study the effectiveness of combining intrathecal radioimmunotherapy and radiation therapy with combination chemotherapy in treating patients who have undergone surgery for medulloblastoma.