PATIENT-SPECIFIC DOSIMETRY OF INDIUM-111-LABELED AND YTTRIUM-90-LABELED MONOCLONAL-ANTIBODY CC49

The objective of this work was to develop patient-specific dosimetry f or patients with metastatic gastrointestinal tract cancers who receive d In-111-CC49 IgG for imaging before therapy with Y-90-CC49 IgG. Metho ds: Whole-body imaging of 12 patients, who received 111-185 MBq (3-5 m Ci) of In-111-CC49, commenced in < 2 hr postinfusion and was continued daily for 4-5 days. SPECT data were acquired at 24 and 72 hr to deter mine the range of In-111-CC49 activity concentrations in tumors and no rmal organs. Time-activity curves were generated from the image data a nd scaled from In-111-CC49 to Y-90-CC49 for dosimetric purposes. Absor bed-dose calculations for Y-90-CC49 included the mean and range in tum or and normal organs. Computed Y-90-CC49 activity concentrations were compared with measurements on 10 needle biopsies of normal liver and f our tumor biopsies. Results: In 9 of 10 normal liver samples, the rang e of computed Y-90-CC49 activity concentrations bracketed measured val ues. This was also the case for 3 of 4 tumor biopsies. Absorbed-dose c alculations for Y-90-CC49 were based on patients' images and activitie s in tissue samples and, hence, were patient-specific. Conclusion: For the radiolabeled antibody preparations used in this study, quantitati ve imaging of In-111-CC49 provided the data required for Y-90-CC49 dos imetry. The range of activities in patients' SPECT images was determin ed for a meaningful comparison of measured and computed values. Knowle dge of activity distributions in tumors and normal organs was essentia l for computing mean values and ranges of absorbed dose and provided a more complete description of the absorbed dose from Y-90-CC49 than wa s possible with planar methods.