title: Correlation of in vivo and in vitro measures of carbonic anhydrase IX antigen expression in renal masses using antibody 124I-cG250.
abstract: 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 (124)I-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 < 0.000001, and with autoradiography of 0.88, P < 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.
  
  
  CONCLUSIONS
  PET/CT can be reliably used to quantify radiolabeled macromolecular uptake in vivo, suggesting important implications for quantitative pharmacokinetic estimates of macromolecular biodistribution.
authors.affiliation: Division of Nuclear Medicine and Clinical Molecular Imaging, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. daniel.pryma@uphs.upenn.edu
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Pryma
authors.forename: Joseph A
authors.initials: JA
authors.lastname: O'Donoghue
authors.forename: John L
authors.initials: JL
authors.lastname: Humm
authors.forename: Achim A
authors.initials: AA
authors.lastname: Jungbluth
authors.forename: Lloyd J
authors.initials: LJ
authors.lastname: Old
authors.forename: Steven M
authors.initials: SM
authors.lastname: Larson
authors.forename: Chaitanya R
authors.initials: CR
authors.lastname: Divgi
mesh_terms: D018262:Adenocarcinoma, Clear Cell / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm / Q000276:immunology*; D001345:Autoradiography; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000276:immunology*; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D010865:Pilot Projects; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D016707:Tissue Fixation; D014055:Tomography, Emission-Computed
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; C106533:G250 monoclonal antibody; D019275:Radiopharmaceuticals; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases