title: FDG PET performed at thyroid remnant ablation has a higher predictive value for long-term survival of high-risk patients with well-differentiated thyroid cancer than radioiodine uptake.
abstract: OBJECTIVE
  The predictive value of FDG PET at thyroid remnant ablation was evaluated in comparison to radioiodine uptake in high-risk patients with differentiated thyroid cancer.
  
  
  METHODS
  One hundred forty-one patients who underwent radioiodine therapy (RIT) after total thyroidectomy and received at least 1 further RIT due to suspected metastases were retrospectively analyzed. Patients had not received RIT previously. FDG PET was performed before thyroid remnant ablation. Thyroid-stimulating hormone-stimulated serum thyroglobulin (Tg) was measured for biochemical response assessment (change of Tg between the first and second RIT, ΔTg).
  
  
  RESULTS
  Biochemical response could be evaluated in 80 patients; survival data could be obtained for 88 patients (maximum, 124 months). Biochemical response was significantly better in patients with radioiodine-positive metastases compared with patients with radioiodine-negative metastases (median ΔTg I+, 55.8% vs I-, 112.6%; P < 0.01). Regarding survival, deaths occurred later in patients with radioiodine-positive metastases compared with radioiodine-negative patients; however, there was no significant difference regarding overall survival (I+, 61.3% vs I-, 58.2%; P > 0.05). Patients with FDG-positive metastases at thyroid remnant ablation showed a poorer biochemical response compared with patients with FDG-negative metastases (median ΔTg FDG+, 77.5% vs FDG-, 53.2%; P < 0.05), and these groups also differed significantly regarding survival (overall survival FDG+, 48.5% vs FDG-, 100%, P < 0.05).
  
  
  CONCLUSIONS
  At thyroid remnant ablation, FDG PET is more predictive for long-term survival, whereas radioiodine uptake is more important for short-term response. FDG PET performed at thyroid remnant ablation might represent a useful tool for management of high-risk patients with differentiated thyroid cancer.
authors.affiliation: From the *Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan; †Department of Nuclear Medicine, Klinikum Rechts der Isar, Technical University Munich, Munich; ‡Department of Nuclear Medicine, University Hospital Bonn, Bonn, Germany; and §Department of Biostatistics, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Florian C
authors.initials: FC
authors.lastname: Gaertner
authors.forename: Shozo
authors.initials: S
authors.lastname: Okamoto
authors.forename: Tohru
authors.initials: T
authors.lastname: Shiga
authors.forename: Yoichi M
authors.initials: YM
authors.lastname: Ito
authors.forename: Yuko
authors.initials: Y
authors.lastname: Uchiyama
authors.forename: Osamu
authors.initials: O
authors.lastname: Manabe
authors.forename: Naoya
authors.initials: N
authors.lastname: Hattori
authors.forename: Nagara
authors.initials: N
authors.lastname: Tamaki
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18