title: 18-fluorodeoxyglucose positron emission tomography in the early diagnostic workup of differentiated thyroid cancer patients with a negative post-therapeutic iodine scan and detectable thyroglobulin.
abstract: BACKGROUND
  Surgery and high-dose radioactive iodine ((131)I) treatment are the cornerstones in the treatment of differentiated thyroid cancer. Patients without (131)I uptake on the post-therapeutic whole body scan (WBS), but with detectable thyroglobulin (Tg) during thyroxine withdrawal (Tg-off), are evaluated with an 18-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET) for tumor localization within three months. The yield of (18)F-FDG-PET imaging and clinical usefulness of a Tg-off cutoff value to predict a positive scan were assessed.
  
  
  METHODS
  From 2002 to 2011, 52 patients with a negative WBS and concurrent detectable Tg-off were evaluated. Thirty-five PET scans were performed during initial treatment, 17 after recurrent disease. Thirty-two patients were on substitution therapy, 17 were evaluated with endogenous thyrotropin elevation, and 3 after recombinant human thyrotropin stimulation. To determine the Tg-off cutoff value, a receiver operating characteristic curve was used.
  
  
  RESULTS
  Nine (17%) (18)F-FDG-PET scans were true positive, 3 (6%) false positive, 36 (69%) true negative, and 4 (8%) false negative (sensitivity 69%, specificity 92%). In 13%, a true-positive scan resulted in a change in the clinical management. The area under the receiver operating characteristic curve is 0.82 [CI 0.64-0.99] (p<0.01), and the Tg-off cutoff value is 38.00 ng/mL (sensitivity 67%, specificity 95%). Ninety percent of (18)F-FDG-PET true-positive patients had a Tg-off >2.00 ng/mL.
  
  
  CONCLUSIONS
  An (18)F-FDG-PET within three months after a negative WBS with detectable Tg-off showed additional tumor localization in 17% of the patients, leading to a change in clinical management in 13%. A clinically useful Tg-off cutoff value was not found, but 90% of positive (18)F-FDG-PET scans occurred in patients with a Tg-off >2.00 ng/mL.
authors.affiliation: Department of Endocrinology, Groningen University Medical Centre, Groningen, The Netherlands.
authors.forename: Deborah
authors.initials: D
authors.lastname: van Dijk
authors.forename: John T M
authors.initials: JT
authors.lastname: Plukker
authors.forename: Ha T T
authors.initials: HT
authors.lastname: Phan
authors.forename: Anneke C
authors.initials: AC
authors.lastname: Muller Kobold
authors.forename: Anouk N A
authors.initials: AN
authors.lastname: van der Horst-Schrivers
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Jansen
authors.forename: Wim J
authors.initials: WJ
authors.lastname: Sluiter
authors.forename: Adrienne H
authors.initials: AH
authors.lastname: Brouwers
authors.forename: Thera P
authors.initials: TP
authors.lastname: Links
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D013972:Thyrotropin
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D013972:Thyrotropin; D013954:Thyroglobulin