Rituximab, Yttrium Y 90 Ibritumomab Tiuxetan in Patients W/Relapsed Stage II, III, or IV Follicular NHL

Inclusion Criteria: * Diagnosis of follicular non-Hodgkin lymphoma (NHL) * Bulky stage II, stage III, or stage IV disease, Bulky disease is defined as any tumor measuring 10.0 cm or more or occupying ≥ one-third of the chest diameter * In first, second, third, or fourth relapse after chemotherapy * Unilateral or bilateral bone marrow aspirate and biopsy with cytogenetics within the past 42 days * Tumor CD20 positive by either flow cytometry or immunoperoxidase staining of paraffin sections using anti-CD20 antibodies * Bidimensionally measurable disease * Patients with non-measurable disease in addition to measurable disease must have all non-measurable disease assessed within the past 42 days * No presence of CNS lymphoma * No chronic lymphocytic leukemia * No HIV- or AIDS-related lymphoma * No presence of pleural effusion * Zubrod performance status 0-2 * ANC ≥ 1,500/μL (unless decreased counts are due to marrow involvement with NHL) * Platelet count \> 100,000/μL (unless decreased counts are due to marrow involvement with NHL) * Serum creatinine ≤ 2.0 mg/dL * Creatinine clearance ≤ 50 mL/min * Serum bilirubin ≤ 2.0 mg/dL * No renal insufficiency or renal failure * No known HIV positivity * Not pregnant or nursing * No prior malignancy except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or other cancer with 5-year disease-free status * No impaired bone marrow reserve, including any of the following: * Hypocellular bone marrow (cellularity ≤ 15%) * Marked ( ≥ 10%) reduction in bone marrow precursors of one or more cell lines (granulocytic, megakaryocytic, erythroid) (beyond that which would be expected for the patient's age and bone marrow cellularity) * History of failed stem cell collection * No serious, non-malignant disease or infection which, in the opinion of the investigator and/or sponsor, would compromise other protocol objectives * At least 3 weeks since all prior therapy (6 weeks for rituximab) and recovered * No prior myeloablative therapies with autologous bone marrow transplantation or peripheral blood stem cell rescue * No prior radioimmunotherapy * No prior external beam radiotherapy to \> 25% of active bone marrow (involved field or regional) * More than 4 weeks since prior major surgery, other than diagnostic surgery Exclusion Criteria Patients with impaired bone marrow reserve, as indicated by one or more of the following: * Platelet count \< 100,000 cells/mm3 * Hypocellular bone marrow (cellularity \< or = 10%) * Marked (\> 10%) reduction in bone marrow precursors of one or more cell lines (granulocytic, megakaryocytic, erythroid) (beyond that which would be expected for the patient's age and bone marrow cellularity * History of failed stem cell collection Prior radioimmunotherapy Presence of CNS lymphoma. Patients must not have clinical evidence of central nervous system (CNS) involvement by lymphoma. Patients with abnormal liver function: total bilirubin \> 2.0 mg/dL Patients with abnormal renal function: serum creatinine \> 2.0 mg/dL or creatinine clearance \< 50 ml/min. Patients who have received prior external beam radiation therapy to \> 25% of active bone marrow (involved field or regional) Patients who have received G-CSF or GM-CSF therapy within 2 weeks prior to treatment Serious nonmalignant disease or infection which, in the opinion of the investigator and/or the sponsor, would compromise other protocol objectives Major surgery, other than diagnostic surgery, within 4 weeks Patients with pleural effusion