<qa>  What is the name of the treatment regimen combined with combination chemotherapy?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. Giving radiation therapy in different ways with combination chemotherapy may kill any remaining tumor cells following surgery. It is not yet known which radiation therapy regimen combined with combination chemotherapy is more effective in treating medulloblastoma. 