title: Do negative 124I pretherapy positron emission tomography scans in patients with elevated serum thyroglobulin levels predict negative 131I posttherapy scans?
abstract: BACKGROUND
  The management of patients with differentiated thyroid cancer (DTC) who have elevated serum thyroglobulin (Tg) levels and negative (131)I or (123)I scans is problematic, and the decision regarding whether or not to administer (131)I therapy (a "blind" therapy) is also problematic. While (124)I positron emission tomography (PET) imaging has been shown to detect more foci of residual thyroid tissue and/or metastases secondary to DTC than planar (131)I images, the utility of a negative (124)I PET scan in deciding whether or not to consider performing blind (131)I therapy is unknown. The objective of this study was to determine whether a negative (124)I pretherapy PET scan in patients with elevated serum Tg levels and negative (131)I or (123)I scans predicts a negative (131)I posttherapy scan.
  
  
  METHODS
  Several prospective studies have been performed to compare the radiopharmacokinetics of (124)I PET versus (131)I planar imaging in patients who 1) had histologically proven DTC, 2) were suspected to have metastatic DTC (e.g., elevated Tg, positive recent fine-needle aspiration cytology, suspicious enlarging mass), and 3) had (131)I planar and (124)I PET imaging performed. Using these criteria, we retrospectively identified patients who had an elevated Tg, a negative diagnostic (131)I/(123)I scan, a negative diagnostic (124)I PET scan, therapy with (131)I, a post-therapy (131)I scan, and a prior (131)I therapy with a subsequent positive post-(131)I therapy scan. For each scan, two readers categorized every focus of (131)I and (124)I uptake as positive for thyroid tissue/metastases or physiological.
  
  
  RESULTS
  Twelve patients met the above criteria. Ten of these 12 patients (83%) had positive foci on (131)I posttherapy scan.
  
  
  CONCLUSIONS
  In our selected patient population, (131)I posttherapy scans are frequently positive in patients with elevated serum Tg levels, a negative diagnostic (131)I or (123)I scan, and a negative (124)I PET scan. Thus, for a patient with elevated serum Tg level, negative diagnostic (131)I planar scan, and a prior post-(131)I therapy scan that was positive, a negative (124)I PET scan will have a low predictive value for a negative post-(131)I therapy scan and should not be used to exclude the option of blind (131)I therapy.
authors.affiliation: 1 Division of Nuclear Medicine, MedStar Washington Hospital Center , Washington, DC.
authors.forename: Gauri R
authors.initials: GR
authors.lastname: Khorjekar
authors.forename: Douglas
authors.initials: D
authors.lastname: Van Nostrand
authors.forename: Carlos
authors.initials: C
authors.lastname: Garcia
authors.forename: Jeffrey
authors.initials: J
authors.lastname: O'Neil
authors.forename: Shari
authors.initials: S
authors.lastname: Moreau
authors.forename: Francis B
authors.initials: FB
authors.lastname: Atkins
authors.forename: Mihriye
authors.initials: M
authors.lastname: Mete
authors.forename: Michael H
authors.initials: MH
authors.lastname: Orquiza
authors.forename: Kenneth
authors.initials: K
authors.lastname: Burman
authors.forename: Leonard
authors.initials: L
authors.lastname: Wartofsky
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D016896:Treatment Outcome; D051598:Whole Body Imaging; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013954:Thyroglobulin