A preliminary survey of 20 patients treated with 90Y-ibritumomab tiuxetan at the Cleveland Clinic Foundation from 1998-2003 detailed patterns of NHL recurrence after treatment. The results of this survey were presented in part by Dr. Macklis at the 2004 annual meeting of the American Society of Therapeutic Radiation Oncology (ASTRO) in Atlanta and recently accepted for publication in the International Journal of Radiation Oncology, Biology, Physics. Based on preliminary data, a hypothesis can be made that some likely sites of disease recurrence/progression after RIT can be predicted by the volume of disease at a specific site prior to RIT. In short, pre-RIT bulky sites of disease are the most likely locations of disease recurrence after RIT followed by gross, but non-bulky, pre-RIT sites followed by entirely new sites. Based on this hypothesis, it might be beneficial to pre-treat bulky sites of NHL with external beam radiotherapy prior to RIT in order to promote a more durable response. Doses of external beam radiation required to consolidate these bulky disease sites are unclear.