TUMOR-ACTIVITY CONFIRMATION AND ISODOSE CURVE DISPLAY FOR PATIENTS RECEIVING IODINE-131-LABELED 16.88-HUMAN MONOCLONAL-ANTIBODY

A study was performed to correlate activity quantitation derived from external imaging with surgical tumor specimens in patients who receive d radiolabeled monoclonal antibody. Patients were given I-131 labeled 16.88 human antibody and scanned 3-5 times by planar and/or single pho ton emission computed tomography imaging methods to acquire time-depen dent activity data in tumor and normal tissues. A method also was deve loped to assess the heterogenous activity distributions in tumor sampl es. Postsurgical tumor and normal tissue samples were subdivided into volume elements (voxels) of 0.5 cm X 0.5 cm X 0.05 cm thick, which wer e used to verify the activity quantitation computed by the conjugate v iew method and to appraise the heterogeneity of radiolabeled antibody uptake. Through the use of the measured voxel activities, along with t he time-dependent activity curves available for the entire tumor speci men derived from imaging, the cumulated activity and absorbed dose for each voxel were uniquely determined. The calculated total absorbed do se values were color-coded as isodose curves and overlaid on a correla ted computed tomographic image. In two patients, activity quantitation derived from external imaging correlated with surgical tumor resectio n specimens within +/- 11%. The tumor-absorbed dose heterogeneity rati o was found to be as high as 10:1, with an average tumor to whore body absorbed dose ratio of 4:1. The mapping of activity with a histologic overlay showed a good correlation among activity uptake, the presence of tumor, and antigen expression on a microscopic scale. The resultan t isodose curves overlaid on correlative computed tomographic scans re present the first images obtained with actual radiolabeled antibody bi odistribution data in patients.