title: Combined PET/CT in the follow-up of differentiated thyroid carcinoma: what is the impact of each modality?
abstract: OBJECTIVE
  18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a well-established method in the follow-up of patients with differentiated thyroid carcinoma (DTC), elevated thyroglobulin (Tg) and negative 131I scans. This retrospective clinical study was designed to evaluate the impact of computed tomography (CT) and that of FDG-PET in combined FDG-PET/CT examinations on the restaging of DTC patients.
  
  
  METHODS
  Forty-seven FDG-PET/CT scans of 33 patients with a history of DTC, elevated Tg levels and negative 131I uptake or additionally suspected 131I-negative lesions were studied. PET and CT images were analysed independently by an experienced nuclear medicine specialist and a radiologist. Afterwards a final consensus interpretation, the gold standard in our department, was provided for the fused PET/CT images and, if available, for supplementary investigations.
  
  
  RESULTS
  Thirty-five investigations (74%) revealed pathological FDG-PET/CT findings. In summary, 25 local recurrences, 62 lymph node metastases and 122 organ metastases (41 lung, 60 bone, 21 other organs) were diagnosed. In 36 out of 47 examinations (77%), the original PET diagnoses were modified in the final consensus interpretation owing to the CT assessments. In 8 of the 35 pathological FDG-PET/CT examinations (23%), the final consensus interpretation of the PET/CT images led to an alteration in the treatment plan.
  
  
  CONCLUSIONS
  PET/CT is a powerful fusion of two pre-existing imaging modalities, which not only improves the diagnostic value in restaging DTC patients with elevated Tg and negative 131I scan, but also provides accurate information regarding subsequent treatment options and may lead to a change in treatment management.
authors.affiliation: Department of Nuclear Medicine and Special Endocrinology, PET/CT Centre, Landeskrankenhaus Klagenfurt, St. Veiter Str. 47, 9020, Klagenfurt, Austria. mzo@gmx.at
authors.forename: Michael
authors.initials: M
authors.lastname: Zoller
authors.forename: Susanne
authors.initials: S
authors.lastname: Kohlfuerst
authors.forename: Isabel
authors.initials: I
authors.lastname: Igerc
authors.forename: Ewald
authors.initials: E
authors.lastname: Kresnik
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Gallowitsch
authors.forename: Iris
authors.initials: I
authors.lastname: Gomez
authors.forename: Peter
authors.initials: P
authors.lastname: Lind
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis* / Q000517:prevention & control*; D011159:Population Surveillance / Q000379:methods; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D018511:Systems Integration; D013964:Thyroid Neoplasms / Q000175:diagnosis*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18