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


CONCLUSIONS
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.
Salvatore
B
B
Fondazione SDN, Naples Italy. barbara.salvatore@libero.it
Paone
G
G
Klain
M
M
Storto
G
G
Nicolai
E
E
D'Amico
D
D
Della Morte
A M
AM
Pace
L
L
Salvatore
M
M
D018263:Adenocarcinoma, Follicular / Q000097:blood / Q000175:diagnosis / Q000628:therapy; D002291:Carcinoma, Papillary / Q000097:blood / Q000175:diagnosis / Q000628:therapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D013965:Thyroidectomy; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin