title: FDG-PET performed concurrently with initial I-131 ablation for differentiated thyroid cancer.
abstract: OBJECTIVE
  Differentiated thyroid cancers (DTCs) are commonly treated by total thyroidectomy followed by I-131 radioiodine ablation to eradicate any residual thyroid tissue and to detect any metastatic lesions on post-treatment whole body scans (TxWBS). However, some DTCs do not trap iodine, resulting in negative whole body scanning. Fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) has proven to be a valuable diagnostic technique for detecting many types of malignant tumors and metastases. The purpose of this study was to evaluate FDG-PET performed concurrently with initial I-131 ablation for its ability to detect lymph node metastasis and for its role in the management of DTC patients.
  
  
  METHODS
  A total of 54 patients (16 males and 38 females; median age = 50 years) with histologically proven DTC underwent both FDG-PET and subsequent I-131 ablation. A dose of 3.7 GBq I-131 was administered to 51 patients, 2.96 GBq was administered to 1 patient, and 2.22 GBq was administered to 2 patients. FDG-PET or PET/CT was performed 3-4 days prior to ablation. TxWBS was conducted 1 week after therapy. FDG-PET scans and TxWBS were interpreted by consensus of 2 experienced radiologists. Serum thyroglobulin (Tg) levels at 3-6 months after ablation were compared between PET-positive and PET-negative patients.
  
  
  RESULTS
  FDG-PET was positive in 25 sites (thyroid bed: n = 9; cervical lymph nodes: n = 12; mediastinal lymph nodes: n = 3; and axillary lymph nodes: n = 1) of 18 patients (33%). Only 5 of 16 lymph nodes (31%) that were PET-positive were also positive on TxWBS. The success rate of Tg-negative after ablation was significantly lower for patients with PET-positive scans than for those with PET-negative scans (p = 0.026).
  
  
  CONCLUSIONS
  FDG-PET performed concurrently with I-131 ablation can detect lymph node metastases in which radioiodine does not accumulate and may influence the management and treatment options for DTC patients.
authors.affiliation: Department of Radiology, Nagoya University Graduate School of Medicine, Shouwa-ku, Nagoya, Japan. iwano45@med.nagoya-u.ac.jp
authors.forename: Shingo
authors.initials: S
authors.lastname: Iwano
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kato
authors.forename: Shinji
authors.initials: S
authors.lastname: Ito
authors.forename: Kenichi
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Shinji
authors.initials: S
authors.lastname: Naganawa
mesh_terms: D055011:Ablation Techniques; D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D012189:Retrospective Studies; D013954:Thyroglobulin / Q000097:blood; D013964:Thyroid Neoplasms / Q000097:blood / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin