Rituximab and Combination Chemotherapy Combined With Yttrium Y 90 Ibritumomab Tiuxetan in Treating Older Patients With Previously Untreated B-Cell Lymphoma

RATIONALE: Monoclonal antibodies such as rituximab and yttrium Y 90 ibritumomab tiuxetan can locate cancer cells and either kill them or deliver radioactive cancer-killing substances to them without harming normal cells. Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Combining rituximab and combination chemotherapy with yttrium Y 90 ibritumomab tiuxetan may kill more cancer cells. PURPOSE: Phase II trial to study the effectiveness of combining rituximab and combination chemotherapy with yttrium Y 90 ibritumomab tiuxetan in treating older patients who have B-cell lymphoma that has not been previously treated.