Comparison of positron emission tomography with [(18)F]FDG and [(68)Ga]DOTATOC in recurrent differentiated thyroid...

The aim of this study was to retrospectively analyse the value of positron emission tomography (PET) with a radiolabelled somatostatin analogue, [(68)Ga]DOTATOC, in recurrent radioiodine positive and negative differentiated thyroid cancer (DTC) compared to [(18)F]FDG PET.

Seventeen patients with known or suspected recurrent DTC were enrolled in this study. All patients underwent PET with [(68)Ga]DOTATOC and [(18)F]FDG under TSH suppressive therapy and whole-body scintigraphy (WBS) after administration of [(131)I] following TSH stimulation. The total number of tumour lesions was defined as the sum of the lesions detected by at least one of these three imaging techniques. Pathologic findings were confirmed histopathologically or by follow-up and conventional radiological imaging.

Both PET tracers consistently detected metastases in 12 patients. In two cases, only [(131)I] WBS and computed tomography revealed metastatic disease; in the remaining three patients with an increased thyroglobulin no correlate could be found. From a total of 104 tumour lesions, [(18)F]FDG PET showed only slightly higher detection rate than [(68)Ga]DOTATOC PET in radioiodine positive patients (28/31 versus 25/31), whereas significant differences were seen in the group with negative [(131)I] WBS (70/73 versus 26/73, P<0.01). Three out of 104 lesions were only visible using [(68)Ga]DOTATOC PET.

[(68)Ga]DOTATOC and [(18)F]FDG PET showed comparable diagnostic performance in recurrent, radioiodine positive DTC. Due to much higher lesion detection rates, [(18)F]FDG PET should be preferred to [(68)Ga]DOTATOC PET in the work-up of radioiodine negative DTC relapse. These preliminary results have to be confirmed by more extensive data in further studies.