- Radioimmunotherapy: Patients receive rituximab IV. Within 4 hours after completion of rituximab, patients receive indium In 111 ibritumomab tiuxetan (imaging dose) IV over 10 minutes on day -25. Patients undergo assessment of biodistribution, imaging, and dosimetry on days -25, -22, and optionally on day -20. Patients with acceptable biodistribution of indium In 111 ibritumomab tiuxetan receive rituximab IV followed by yttrium Y 90 ibritumomab tiuxetan (therapeutic dose) IV over 10 minutes on day -18.