Fluorodeoxyglucose PET/CT in patients with differentiated thyroid cancer and elevated thyroglobulin after total thyroidectomy and (131)I ablation

Q J Nucl Med Mol Imaging. 2008 Mar;52(1):2-8.

Abstract

Aim: The aim of this study was to evaluate the role of 18F fluorodeoxyglucose-positron emission tomography (FDG-PET), differentiated thyroid carcinoma (DTC) treated with therapeutic (131)I because of elevated thyroglobulin (Tg) levels during follow up. The results of FDG-PET/CT were compared with post-therapy (131)I whole body scan (131I-t-WBS) and Tg at short term follow up.

Methods: Forty-five patients with DTC underwent a new therapeutic (131I) administration based upon Tg values >1.5 ng/mL. All patients underwent (131I-t-WBS) 5-7 days after 131I therapy. A few days before 131I administration, a FDG-PET scan was performed in all patients. FDG-PET/CT was considered positive (PET+) when at least one abnormal focus of FDG uptake was found; likewise, 131I-t-WBS was considered positive(WBS+) when at least on abnormal focus of uptake was found. Assessment of short-term response to radioiodine was performed by measuring Tg values.

Results: FDG-PET/CT was positive in 32 patients, 23 of which had positive 131I-t-WBS and negative in 13, 8 of which had a negative 131I-t-WBS. Overall agreement was 69%. Tg values were significantly higher in FDG-PET/CT positive (502+/-1 027 ng/mL) than in FDG-PET/CT negative patients (57+/-94 ng/mL). A significant difference emerged between 131I-t-WBS positive (561 +/- 1 086 ng/mL) and 131I-t-WBS negative (65+/- 120 ng/mL) findings. In these 45 patients Tg normalized in 36%, was reduced by at least 50% in 24% and remained unchanged in the remaining 40%. Overall, at short-term follow-up, Tg values normalized in 77% of the 13 patients with negative FDG-PET/CT and in 19% of the 32 patients with positive FDG-PET/CT.

Conclusion: FDG-PET/CT is a powerful and useful tool for assessing patients with DTC. it can provide additional information in those patients with high Tg at follow-up and eligible for 131I therapy. A negative FDG-PET/CT could also represent a prognostic tool combined with serum Tg testing a short term follow-up.

MeSH terms

  • Adenocarcinoma, Follicular / blood
  • Adenocarcinoma, Follicular / diagnosis
  • Adenocarcinoma, Follicular / therapy
  • Carcinoma, Papillary / blood
  • Carcinoma, Papillary / diagnosis
  • Carcinoma, Papillary / therapy
  • Female
  • Fluorodeoxyglucose F18*
  • Humans
  • Image Processing, Computer-Assisted
  • Iodine Radioisotopes / therapeutic use*
  • Male
  • Middle Aged
  • Positron-Emission Tomography*
  • Radiopharmaceuticals*
  • Thyroglobulin / blood*
  • Thyroid Neoplasms / blood
  • Thyroid Neoplasms / diagnosis*
  • Thyroid Neoplasms / therapy
  • Thyroidectomy*
  • Tomography, X-Ray Computed*
  • Whole Body Imaging

Substances

  • Iodine Radioisotopes
  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18
  • Thyroglobulin