title: Does recombinant human thyrotropin-stimulated positron emission tomography with [18F]fluoro-2-deoxy-D-glucose improve detection of recurrence of well-differentiated thyroid carcinoma in patients with low serum thyroglobulin?
abstract: BACKGROUND
  Thyrotropin (TSH) stimulates thyrocyte metabolism, glucose transport, and glycolysis. The interest in using recombinant human TSH (rhTSH) stimulation of fluoro-2-deoxy-D-glucose (FDG) with positron emission tomography (PET) has been shown, but mainly for patients with high serum thyroglobulin (Tg) concentration. We evaluated the use of rhTSH-stimulated PET-FDG in patients with low serum Tg concentration.
  
  
  METHODS
  Sixty-one PET/computed tomography (CT)-FDG (Biograph Sensation 16; Siemens Medical Solutions, Knoxville, TN) were performed in 44 patients (28 women and 16 men; 51 +/- 16 years) with positive Tg levels, negative or no contributive iodine-131 whole-body scintigraphy results, and no contributive morphological imaging results (ultrasound, magnetic resonance imaging, and CT). Thirty-eight patients had papillary carcinoma and six had follicular thyroid carcinoma. All patients had previously undergone total thyroidectomy and postoperative iodine ablation of thyroid bed remnant tissue. The rhTSH-stimulated PET/CT-FDG (5 MBq/kg) was performed after two 0.9 mg intramuscular doses of rhTSH (Thyrogen; Genzyme) which were administered 48 and 24 hours before imaging, while patients continued levothyroxine (LT(4)). Blood sampling was performed immediately before FDG injection for measurement of serum TSH and Tg concentrations (TSH(1) and Tg(1)) and after 48 hours (TSH(2) and Tg(2)). PET/CT-FDG findings were compared with the Tg: (i) at the initial iodine treatment during T(4) withdrawal (Tg(ini)), (ii) under T(4) (Tg(T4)) within 3 months before the PET/CT-FDG, (iii) with Tg(1), and (iv) with Tg(2). PET/CT-FDG findings were correlated with the findings of histology, iodine-131 whole-body scintigraphy, morphological imaging, or clinical follow-up.
  
  
  RESULTS
  The mean Tg(ini) was 785 +/- 2707 microg/L for a TSH of 73 +/- 64 mU/L. The mean Tg(T4) was 7 +/- 15 microg/L (T(4) = 195 +/- 59 microg/day; mean TSH of 0.24 +/- 0.57 mU/L). Among the 44 patients, PET/CT-FDG findings were positive in 20 and negative in 24. Among the 61 PET/CT-FDG, 25 PET/CT-FDG were positive (41%). Among the 25 positive PET, the Tg(T4) values were less than 10 microg/L for 19, including 9 true-positive patients (20% of the 44 patients). There was no difference of PET/CT-FDG results (positive vs. negative) as related to the serum Tg concentrations (p = 0.99 for Tg(ini), p = 0.95 for Tg(T4), p = 0.07 for Tg(1), and p = 0.42 for Tg(2)). No relation was observed with PET/CT-FDG results and initial tumor size (p = 0.52) or node metastasis (p = 0.14).
  
  
  CONCLUSIONS
  In the diagnosis of recurrent disease in patients with differentiated thyroid carcinoma and low Tg level, the sensitivity of rhTSH-stimulated PET/CT-FDG seems to be low and no correlation was observed between PET/CT-FDG findings and Tg level. However, positive PET-FDG results have been found in 9/44 (20%) patients with serum Tg levels lower than 10 microg/L. Therefore, this series shows that a cutoff value of 10 microg/L for the Tg under T(4) is probably not the best criteria to select patient candidates for PET/CT-FDG examination to detect the recurrence of differentiated thyroid carcinoma.
authors.affiliation: Department of Nuclear Medicine, Henri Becquerel Centre and Rouen University Hospital, University of Rouen, Rouen, France. pierre.vera@rouen.fnclcc.fr
authors.forename: Pierre
authors.initials: P
authors.lastname: Vera
authors.forename: Caroline
authors.initials: C
authors.lastname: Kuhn-Lansoy
authors.forename: Agathe
authors.initials: A
authors.lastname: Edet-Sanson
authors.forename: Sebastien
authors.initials: S
authors.lastname: Hapdey
authors.forename: Romain
authors.initials: R
authors.lastname: Modzelewski
authors.forename: Anne
authors.initials: A
authors.lastname: Hitzel
authors.forename: Joelle
authors.initials: J
authors.lastname: d'Anjou
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Basuyau
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000532:radiotherapy / Q000601:surgery; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D002648:Child; D004334:Drug Administration Schedule; D005260:Female; D019788:Fluorodeoxyglucose F18; D020249:Hormone Replacement Therapy; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000000981:diagnostic imaging*; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography / Q000379:methods*; D011994:Recombinant Proteins; D013954:Thyroglobulin / Q000097:blood* / Q000172:deficiency; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000601:surgery; D013965:Thyroidectomy; D013972:Thyrotropin / Q000008:administration & dosage / Q000097:blood / Q000235:genetics; D013974:Thyroxine / Q000627:therapeutic use; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D019788:Fluorodeoxyglucose F18; D013972:Thyrotropin; D013954:Thyroglobulin; D013974:Thyroxine