High-Dose Y-90-Ibritumomab Tiuxetan Added to Reduced-Intensity Allogeneic Stem Cell Transplant Regimen for Relapsed or Refractory Aggressive B-Cell Lymphoma

PRIMARY OBJECTIVES: I. To assess the safety and efficacy of 1.5 mCi/kg (max 120 mCi) 90Y-Ibritumomab tiuxetan (yttrium Y 90 ibritumomab tiuxetan) (anti-CD20) combined with fludarabine (fludarabine phosphate) (30 mg/m\^2 x 3) and 2 gray (Gy) total body irradiation followed by human leukocyte antigens (HLA) matched allogeneic hematopoietic transplantation for patients with relapsed or refractory aggressive B-cell lymphoma. OUTLINE: Beginning 24-48 hours prior to therapy infusion, patients receive rituximab intravenously (IV) over 4-6 hours and then receive a therapy-dose of high-dose yttrium Y 90 ibritumomab tiuxetan IV over 30 minutes on day -14 prior to transplant. Patients also receive fludarabine phosphate IV on days -4 to -2 and undergo TBI followed by allogeneic PBSCT on day 0. Patients also receive cyclosporine orally (PO) twice daily (BID) on days -3 to 56 with taper to day 180 (related donor) or -3 to 100 with taper over 11 weeks (unrelated donor) and mycophenolate mofetil PO BID on days 0-27 (related donor) or PO thrice daily (TID) on days 0-40 with taper to day 96 (unrelated donor). After completion of study treatment and assessments through \~day 100 following transplant, patients are followed up at 1, 3, 6, and 12 months and then annually up to 2 years thereafter.