[68Ga]DOTATATE PET/MRI and [18F]FDG PET/CT are complementary and superior to diffusion-weighted MR imaging for radioactive-iodine-refractory differentiated thyroid cancer
The purpose of this study was to determine whether [68Ga]DOTATATE PET/MRI with diffusion-weighted imaging (DWI) can replace or complement [18F]FDG PET/CT in patients with radioactive-iodine (RAI)-refractory differentiated thyroid cancer (DTC). The study population comprised 12 patients with elevated thyroglobulin and a negative RAI scan after thyroidectomy and RAI remnant ablation who underwent both [18F]FDG PET/CT and [68Ga]DOTATATE PET/MRI within 8 weeks of each other. The presence of recurrent cancer was evaluated on a per-patient, per-organ and per-lesion basis. Histology, and prior and follow-up examinations served as the standard of reference. Recurrent or metastatic tumour was confirmed in 11 of the 12 patients. [68Ga]DOTATATE PET(/MRI) correctly identified the tumour burden in all 11 patients, whereas in one patient local relapse was missed by [18F]FDG PET/CT. In the lesion-based analysis, overall lesion detection rates were 79/85 (93 %), 69/85 (81 %) and 27/82 (33 %) for [18F]FDG PET/CT, [68Ga]DOTATATE PET/MRI and DWI, respectively. [18F]FDG PET(/CT) was superior to [68Ga]DOTATATE PET(/MRI) in the overall evaluation and in the detection of pulmonary metastases. In the detection of extrapulmonary metastases, [68Ga]DOTATATE PET(/MRI) showed a higher sensitivity than [18F]FDG PET(/CT), at the cost of lower specificity. DWI achieved only poor sensitivity and was significantly inferior to [18F]FDG PET in the lesion-based evaluation in the detection of both extrapulmonary and pulmonary metastases. [18F]FDG PET/CT was more sensitive than [68Ga]DOTATATE PET/MRI in the evaluation of RAI-refractory DTC, mostly because of its excellent ability to detect lung metastases. In the evaluation of extrapulmonary lesions, [68Ga]DOTATATE PET(/MRI) was more sensitive and [18F]FDG PET(/CT) more specific. Furthermore, DWI did not provide additional information and cannot replace [18F]FDG PET for postoperative monitoring of patients with suspected RAI-refractory DTC.