Gamma camera scans and pretreatment tumor volumes as predictors of response and progression after Y-90 anti-CD20 radioimmunotherapy.

PURPOSE: To evaluate two potential approaches to predicting site-specific patterns of recurrence after yttrium-90 ibritumomab tiuxetan radioimmunotherapy (RIT) for CD20+ B-cell Non-Hodgkin's lymphoma. These predictive methods may be useful in evaluating the utility of local intensification of individual nodal or extranodal sites using external beam radiotherapy. METHODS AND MATERIALS: Records and images were evaluated for 20 patients previously treated with yttrium-90 ibritumomab RIT. Intensity of isotope uptake on the pretreatment two-dimensional antibody scans and maximal extent of tumor deposits found on computed tomography images of each anatomic site were correlated with response and subsequent patterns of recurrence or progression.
RESULTS: Our data failed to suggest a significant correlation between the site-by-site two-dimensional image intensity on the pre-RIT scan and the likelihood of response at those sites. In contrast, an analysis of pretreatment target volumes did correlate significantly with progression. A collective analysis of disease sites from all 20 patients found that 83% (10/12) sites of "bulky" (maximal diameter > or = 5 cm) disease displayed evidence of progression vs. 28% (26/93) of "nonbulky" disease sites containing gross disease but no area measuring >5 cm (p < 0.001). All patients with at least one site of bulky disease had initial disease progression occur at a bulky site, with a bulky site being the sole first site of progression in approximately 50%. In patients with only nonbulky disease sites, approximately one third progressed initially at an entirely new site of disease.
CONCLUSION: We conclude that we can use tumor bulk to establish a statistical hierarchy of likely tumor progression sites and use this pattern to direct the use of additional external beam radiotherapy to augment treatment.