PT - JOURNAL ARTICLE AU - Daniel A. Pryma AU - Joseph A. O'Donoghue AU - John L. Humm AU - Achim A. Jungbluth AU - Lloyd J. Old AU - Steven M. Larson AU - Chaitanya R. Divgi TI - Correlation of In Vivo and In Vitro Measures of Carbonic Anhydrase IX Antigen Expression in Renal Masses Using Antibody <sup>124</sup>I-cG250 AID - 10.2967/jnumed.110.083295 DP - 2011 Apr 01 TA - Journal of Nuclear Medicine PG - 535--540 VI - 52 IP - 4 4099 - http://jnm.snmjournals.org/content/52/4/535.short 4100 - http://jnm.snmjournals.org/content/52/4/535.full SO - J Nucl Med2011 Apr 01; 52 AB - The goal of this study was to determine whether there is a potential correlation between quantification of radiolabeled macromolecular uptake in tumors determined in vivo using PET/CT and in vitro using autoradiography and γ-counting of tumor tissue. Methods: Twenty-six patients with renal masses scheduled for surgical resection received 124I-labeled antibody cG250. Tumor specimens obtained from resection were studied. Fifteen of these patients had clear cell cancer demonstrated by positive findings on PET/CT images and histopathology. Radioactivity in tumors was measured on PET/CT images and expressed as percentage injected dose per gram. These values were then normalized to measurements of known serum radioactivity from a venous blood sample obtained at the time of PET/CT. Comparable measurements were obtained in vitro using γ-well counting and digital autoradiography of tumor tissue. Results: There was a significant correlation between tumor radioactivity estimated in vivo and in vitro (Spearman correlation coefficient comparing normalized PET measurements with well counting of 0.84, P &lt; 0.000001, and with autoradiography of 0.88, P &lt; 0.000001). PET/CT measurements of tumor uptake were lower than measurements obtained with either of the in vitro methods, and digital autoradiography resulted in the highest measurements. Conclusion: PET/CT can be reliably used to quantify radiolabeled macromolecular uptake in vivo, suggesting important implications for quantitative pharmacokinetic estimates of macromolecular biodistribution.