Radiation Therapy With or Without Chemotherapy in Treating Patients With Anaplastic Oligodendroglioma

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining chemotherapy with radiation therapy may kill more tumor cells. PURPOSE: Randomized phase III trial to compare the effectiveness of radiation therapy with or without chemotherapy in treating patients who have anaplastic oligodendroglioma.