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

DISEASE CHARACTERISTICS: * Histologically confirmed diffuse large B-cell lymphoma, including any of the following subtypes: * Centroblastic * Immunoblastic * T-cell/histiocyte-rich * Lymphomatoid granulomatosis type * Anaplastic large B-cell * Plasmablastic * Mediastinal * Intravascular large B-cell lymphoma * Previously untreated * High-intermediate or high-risk disease, defined by an age-adjusted international prognostic index score of 2 or 3 (with 1 point each assigned for a ECOG greater than 1/Karnofsky less than 80%, lactate dehydrogenase greater than normal, and stage III or IV) * Lymphomas with discordant histology and a diffuse large B-cell component are eligible * Must have an initial diagnostic specimen that is CD20+ * At least Ann Arbor stage II disease * No confinement of disease to an involved-field radiotherapy port (stage I or limited stage II disease) * Bidimensionally measurable disease with at least 1 lymph node at least 2.0 cm by 2.0 cm by physical examination, CT scan, or positron-emission tomography * Bone marrow cellularity greater than 15% * No known brain or leptomeningeal metastases * No primary effusion lymphomas PATIENT CHARACTERISTICS: Age * 60 and over\* NOTE: \*Patients 60 to 65 years of age must be deemed ineligible for autologous stem cell transplantation Performance status * Karnofsky 50-100% Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Bilirubin no greater than 2.0 mg/dL (except for Gilbert's disease) Renal * Creatinine no greater than 1.5 mg/dL\* OR * Creatinine clearance greater than 50 mL/min\* NOTE: \*Patients not meeting either criterion but who have renal insufficiency directly related to lymphomatous involvement of the kidneys or renal collecting system are allowed Cardiovascular * Cardiac ejection fraction at least 50% by echocardiogram * No acute myocardial infarction within the past 3 months * No uncontrolled hypertension * No New York Heart Association class III or IV congestive heart failure * No unstable angina pectoris Other * Not pregnant or nursing * Fertile patients must use effective contraception * HIV negative * B12 and folate greater than the lower limit of normal * Transferrin saturation at least 15% * Ferritin greater than 10 µg/L * At least 6 weeks since prior RBC donation * No active seizure disorder * Prior seizure disorder allowed if free of antiseizure medication and evidence of seizure activity for the past 5 years * No concurrent uncontrolled medical problems that would preclude administration of chemotherapy or radioimmunotherapy * No other concurrent malignancy treated with chemotherapy or radiotherapy except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix PRIOR CONCURRENT THERAPY: Biologic therapy * At least 4 weeks since prior RBC transfusion * No prior biologic therapy * No other concurrent biologic therapy Chemotherapy * No prior chemotherapy (one course of R-CHOP allowed) * No other concurrent standard or investigational chemotherapy Endocrine therapy * No more than 7 consecutive days of prior steroids (premedication allowed for prior intravenous contrast allergy) * No other concurrent corticosteroids Radiotherapy * No prior radiotherapy Surgery * Not specified