Chemotherapy and Whole-Brain Radiation Therapy in Treating Patients With Primary Central Nervous System Non- Hodgkin's Lymphoma

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 radiation therapy with chemotherapy may kill more tumor cells and may be an effective treatment for non-Hodgkin's lymphoma. PURPOSE: Phase II trial to study the effectiveness of combination chemotherapy and whole-brain radiation therapy in patients with primary central nervous system non-Hodgkin's lymphoma.