Purpose of the Study
In this retrospective study, we reported our experience with FDG-PET/CT in evaluation of medullary thyroid cancer
(MTC) patients with persistent elevated calcitonin levels.
Materials and Methods
A total of 33 F-18 FDG PET/CT scans and 9 somatostatin receptor imaging (SRI) (6 In-111 octreotide and 3 Ga-68
DOTATATE PET/CT) of 25 MTC patients with persistently elevated calcitonin levels, performed for staging and
restaging, were analyzed retrospectively. The scans were compared lesion by lesion with histopathological data and
other imaging methods. Because all patients had abnormally high calcitonin levels defined as persistent disease,
negative F-18 FDG PET/CT scans accepted as false negative. Because there was no true-negative study, only sensitivity
and positive predictive value (PPV) were calculated. Calcitonin levels and SUVmax values were assessed by Mann-
Whitney U test and the ROC curve analysis.
There were 11 true-positive, 11 false-positive and 11 false-negative F-18 FDG PET/CT scans. Sensitivity and PPV
were 50% and 50% respectively. Difference of mean calcitonin level between true-positive cases and the
others was nonsignificant. SUVmax of true-positive lesions were significantly higher than of the others. All 9 SRIs
FDG PET/CT scan appeared to be less sensitive. However, it should be considered that F-18 FDG PET/CT was
performed to the patients with only no lesion had been detected by the other imaging modalities in this group.
Because F-18 FDG PET/CT was not performed when a residual or recurrent lesion had clearly been detected before,
sensitivity of 50% was considered to be acceptable.