There is a lack of efficacious treatment options for patients with relapsed/refractory diffuse large cell Non-Hodgkin's lymphoma (DLCL) who are not appropriate candidates for stem cell transplantation. DLCL is a relatively radiosensitive disease and patients with DLCL have been reported to respond to anti-CD20 monoclonal antibody (MAB) therapy. Therefore, radioimmunotherapy targeting CD20 is a rational and promising therapeutic approach for this patient population.