Patient-Specific Dosimetry of Indium-111- and Yttrium-90-Labeled Monoclonal Antibody CC49

The objective of this work was to develop patient-specific dosimetry for patients with metastatic gastrointestinal tract cancers who re ceived 111ln-CC49IgG for imaging before therapy with 90Y-CC49 IgG. Methods: Whole-body imaging of 12 patients, who received 111-185 MBq (3-5 mCi) of 111ln-CC49, commenced in < 2 hr postinfusion and was continued daily for 4-5 days. SPECT data were acquired at 24 and 72 hr to determine the range of111ln-CC49 activity concentrations in tumors and normal organs. Time-activity curves were generated from the Âimagedata and scaled from 111ln-CC49to 90Y-CC49for dosimetrie purposes. Absorbed-dose calculations for 90Y-CC49 included the mean and range in tumor and normal organs. Computed 90Y-CC49 activity concentrations were compared with measurements on 10 needle biopsies of normal liver and four tumor biopsies. Results: In 9 of 10 normal liver samples, the range of computed 90Y-CC49 activity concentrations bracketed measured values. This was also the case for 3 of 4 tumor biopsies. Absorbed-dose calculations for 90Y-CC49were based on patients' images and activities in tissue samples and, hence, were patient-specific. Conclusion: For the radiolabeled antibody prepa rations used in this study, quantitative imaging of 111ln-CC49pro vided the data required for 90Y-CC49 dosimetry. The range of activities in patients' SPECT images was determined for a mean ingful comparison of measured and computed values. Knowledge of activity distributions in tumors and normal organs was essential for computing mean values and ranges of absorbed dose and provided a more complete description of the absorbed dose from 90Y-CC49 than was possible with planar methods.