PT - JOURNAL ARTICLE AU - George Sgouros AU - Shannon Squeri AU - Åse M. Ballangrud AU - Katherine S. Kolbert AU - Jerrold B. Teitcher AU - Katherine S. Panageas AU - Ronald D. Finn AU - Chaitanya R. Divgi AU - Steven M. Larson AU - Andrew D. Zelenetz TI - Patient-Specific, 3-Dimensional Dosimetry in Non-Hodgkin’s Lymphoma Patients Treated with <sup>131</sup>I-anti-B1 Antibody: Assessment of Tumor Dose-Response DP - 2003 Feb 01 TA - Journal of Nuclear Medicine PG - 260--268 VI - 44 IP - 2 4099 - http://jnm.snmjournals.org/content/44/2/260.short 4100 - http://jnm.snmjournals.org/content/44/2/260.full SO - J Nucl Med2003 Feb 01; 44 AB - A comprehensive, SPECT-based, patient-specific 3-dimensional (3D) dosimetry analysis has been performed using 3D-ID, a previously developed software package. The role of the total-body tumor burden, individual lesion size, tumor absorbed dose, and the spatial distribution of the absorbed dose on response and on the time course of tumor shrinkage has been examined in patients with lymphoma treated by radioimmunotherapy. Methods: Data from 15 patients participating in a phase II study of 131I-labeled anti-B1 antibody (tositumomab) were used. Patients were administered a tracer dose of 131I for imaging and pharmacokinetics. Dose estimates from the tracer studies were used to prescribe the therapeutic administration such that the whole-body absorbed dose did not exceed 75 cGy. All patients received a fixed mass amount of antibody for both the tracer and the therapeutic administrations. SPECT and planar imaging were performed 3–4 d after the therapeutic administration. CT or MRI scans were available on all patients. Total tumor burden was assessed by drawing contours around all lymphoma lesions identified on whole-body CT or MRI. Mean absorbed doses were estimated for selected, index lesions by conventional dosimetry and also by 3D SPECT-based dosimetry. Using a patient-specific dosimetry package, 3D-ID, dose-volume histograms were also generated to assess the spatial distribution of absorbed dose. This approach made it possible to obtain estimates of the minimum and maximum absorbed doses for individual tumors in addition to the mean. Results: Mean absorbed dose estimates obtained by patient-specific SPECT-based dosimetry using 3D-ID were within 2%–5% of estimates obtained by conventional dosimetry. None of the absorbed dose parameters (mean, minimum, maximum, uniformity) were found to have a significant correlation with tumor response. The total-body tumor burden did not impact on overall response or toxicity. Conclusion: This analysis represents the first full reported implementation of a patient-specific 3D dosimetry package. The absence of a dose-response relationship for tumors is surprising and suggests that absorbed dose is not the sole determinant of tumor response in these patients. The absence of a correlation between the total-body tumor burden and overall response or toxicity suggests that tailoring the milligram amount of administered antibody to patient tumor burden is not likely to improve response or reduce toxicity.