CT-SPECT FUSION PLUS CONJUGATE VIEWS FOR DETERMINING DOSIMETRY IN IODINE-131-MONOCLONAL ANTIBODY THERAPY OF LYMPHOMA PATIENTS

A method for performing I-131 quantitative SPECT imaging is described which uses the superimposition of markers placed on the skin to accomp lish fusion of computed tomography (CT) and SPECT image sets. Methods: To calculate mean absorbed dose after administration of one of two I- 131-labeled monoclonal antibodies (Mabs), the shape of the time-activi ty curve is measured by daily diagnostic conjugate views, the y-axis o f that curve is normalized by a quantitative SPECT measurement (usuall y intra-therapy), and the tumor mass is deduced from a concurrent CT v olume measurement. The method is applied to six B-cell non-Hodgkin's l ymphoma patients. Results: For four tumors in three patients treated w ith the MB1 Mab, a correlation appears to be present between resulting mean absorbed dose and disease response. Including all dosimetric est imates for both antibodies, the range for the specific absorbed dose i s within that found by others in treating B-cell lymphoma patients. Ex cluding a retreated anti-B1 patient, the tumor-specific absorbed dose during anti-B1 therapy is from 1.4 to 1.7 mGy/MBq. For the one anti-B1 patient, where quantitative SPECT and conjugate-view imaging was carr ied out back to back, the quantitative SPECT-measured activity was som ewhat less for the spleen and much less for the tumor than that from c onjugate views. Conclusion: The quantitative SPECT plus conjugate view s method may be of general utility for macro-dosimetry of I-131 therap ies.