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B-Cell Non-Hodgkin Lymphoma: PET/CT Evaluation after ⁹⁰Y–Ibritumomab Tiuxetan Radioimmunotherapy—Initial Experience¹

¹ From the Department of Radiology, University of Southern California, 1200 N State St, GNH 3550, Los Angeles, CA 90033. From the 2005 RSNA Annual Meeting. Received April 2, 2006; revision requested June 5; revision received May 14, 2007; accepted June 13; final version accepted August 1. Address correspondence to G.A.U. (e-mail: ulaner{at}usc.edu).

Purpose: To retrospectively compare fusion fluorine 18 fluorodeoxyglucose (FDG) positron emission tomographic (PET)/computed tomographic (CT) imaging with CT imaging alone in the evaluation of yttrium 90 (⁹⁰Y)–ibritumomab tiuxetan radioimmunotherapy treatment of B-cell non-Hodgkin lymphoma.

Materials and Methods: This HIPAA-compliant study was performed with approval from the University of Southern California Institutional Review Board and with informed consent. Five men and five women (mean age, 52 years; range, 38–70 years) with relapsed or refractory non-Hodgkin lymphoma underwent FDG PET/CT imaging both 14–27 days before treatment with ⁹⁰Y–ibritumomab tiuxetan and 4–6 months after treatment. Response after treatment was measured with CT imaging as complete response, partial response, or stable or progressive disease, as defined according to published criteria from a National Cancer Institute–sponsored international workshop. Response after treatment was measured with PET as complete response, partial response, or stable or progressive disease, as defined according to published criteria of the European Organization for Research and Treatment of Cancer. Responses were determined by three interpreters in consensus.

Results: Interpretation of CT images alone resulted in classification of eight (80%) of 10 patients as responders to treatment, with two patients (20%) classified as having complete response. At reevaluation with fused PET/CT images, two patients (20%) had residual lesions at CT that did not show evidence of FDG avidity. These two patients, classified as partial responders according to CT criteria alone, were classified as complete responders at PET/CT. Both of these patients were free of evident disease at 18 or more months of follow-up.

Conclusion: The use of combined FDG PET/CT may enable superior assessment of response to ⁹⁰Y–ibritumomab tiuxetan treatment than the use of CT alone, at which one may underestimate ⁹⁰Y–ibritumomab tiuxetan response by considering inactive residual CT masses to be residual disease.

© RSNA, 2008