Radiation Therapy Plus Combination Chemotherapy in Treating Children With Medulloblastoma

RATIONALE: 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 radiation therapy with chemotherapy may kill more tumor cells. It is not yet known which chemotherapy regimen is more effective when combined with radiation therapy for treating medulloblastoma. PURPOSE: Randomized phase III trial to compare two combination chemotherapy treatments plus radiation therapy in treating children with newly diagnosed medulloblastoma.