Correlation between metabolic uptake of F-18-FDG-PET/computed tomography and thyroglobulin level in differentiated thyroid cancer patients with suspected recurrence

Our objective is to determine if there is correlation between serum thyroglobulin and SUVmax of the main lesion detected in F18-FDG-PET/CT scan, in differentiated thyroid cancer (DTC) patients with suspected recurrence.

All DTC patients enrolled in this prospective study, received at least one dose of radioactive iodine. During follow-up, they are suspected to have a recurrence due to elevated tumor markers although negative iodine whole-body scans. For all patients, F18-FDG-PET/CT scanning was performed. A 3D volume of interest was generated over the liver and main lesion to obtain maximum standardized uptake value (SUVmax). We calculated the lesion/liver ratio. Follow-up and/or histopathological examination were the gold standard. Pearson's correlation coefficient was calculated between thyroglobulin and SUVmax of the main lesion.

Sixty-eight patients were recruited in this study. F18-FDG-PET/CT identified suspicious malignant lesions in 42 patients, equivocal in 18 patients, while 8 patients showed no abnormal findings. Fifty-two, 6, 8, and 2 patients were true positive, true negative, false positive, and false negative respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 72%, 57% 87%, 35%, and 69% respectively. The median SUVmax and lesion/liver ratio were significantly higher in the malignant lesions than that of benign lesions (3.9 vs. 1.3 and 1.45 vs. 0.54 respectively). We found that the main lesion SUVmax and lesion/liver ratio have a positive moderate correlation with thyroglobulin (0.338 and 0.325 respectively).

In DTC patients with suspected recurrence, SUVmax of F18-FDG-PET/CT lesion showed a moderate positive correlation with serum thyroglobulin.