B-Cell Non-Hodgkin Lymphoma: PET/CT Evaluation after90Y–Ibritumomab Tiuxetan Radioimmunotherapy—Initial Experience1

Abstract

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 ((90)Y)-ibritumomab tiuxetan radioimmunotherapy treatment of B-cell non-Hodgkin lymphoma. 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 (90)Y-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. 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. The use of combined FDG PET/CT may enable superior assessment of response to (90)Y-ibritumomab tiuxetan treatment than the use of CT alone, at which one may underestimate (90)Y-ibritumomab tiuxetan response by considering inactive residual CT masses to be residual disease.