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 received ¹¹¹In-CC49 IgG for imaging before therapy with ⁹⁰Y-CC49 IgG. Methods: Whole-body imaging of 12 patients, who received 111-185 MBq (3-5 mCi) of ¹¹¹In-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 of ¹¹¹In-CC49 activity concentrations in tumors and normal organs. Time- activity curves were generated from the image data and scaled from ¹¹¹In- CC49 to ⁹⁰Y-CC49 for dosimetric 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 tour 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-CC49 were based on patients' images and activities in tissue samples and, hence, were patient- specific. Conclusion: For the radiolabeled antibody preparations used in this study, quantitative imaging of ¹¹¹In-CC49 provided the data required for ⁹⁰Y-0C49 dosimetry. The range of activities in patients' SPECT images was determined for a meaningful 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.