Purpose: This was a retrospective study to detect and map the extent of disease in recurrent medullary thyroid carcinoma (MTC) using the novel PET somatostatin analogue (68)Ga-DOTATATE and conventional (18)F-FDG positron emission tomography/computed tomography (PET/CT).
Methods: Eighteen patients (13 men, 5 women, median age: 54 years) who had previously been operated on for MTC and presented with biochemical (raised calcitonin levels) and/or imaging evidence of recurrence underwent both (68)Ga-DOTATATE and (18)F-FDG PET/CT within a maximum interval of 4 weeks (median interval of 1 week). (68)Ga-DOTATATE- and (18)F-FDG-avid lesions were recorded per patient as well as per region in six distinct regions: (1) thyroid bed-local recurrence, (2) cervical lymph nodes, (3) mediastinum, (4) lungs, (5) liver and (6) bones. The (68)Ga-DOTATATE and (18)F-FDG PET/CT findings were classified as positive or negative on visual interpretation. These findings were further characterised as concordant or discordant, depending on whether there was agreement or discrepancy in imaging with the two radiotracers. A separate analysis of the unenhanced CT component of the examination was performed. Verification of the lesions was achieved by histopathological analysis, further imaging studies and clinical follow-up.
Results: (68)Ga-DOTATATE PET/CT imaging achieved disease detection in 13 of 18 and (18)F-FDG PET/CT in 14 of 18 patients. These results corresponded to per-patient sensitivities of 72.2% [95% confidence interval (CI): 46.4-89.3%] for (68)Ga-DOTATATE versus 77.8% (95% CI: 51.9-92.6%) for (18)F-FDG (non-significant difference). (18)F-FDG revealed a total of 28 metastatic MTC regions and (68)Ga-DOTATATE 23 regions. In ten patients a discordant tracer pattern of per-region and/or per-lesion distribution of recurrent disease was observed, while in four patients a concordant pattern was noted (no lesions were detected by either modality in the remaining four patients).
Conclusion: Neither (18)F-FDG nor (68)Ga-DOTATATE PET/CT can fully map the extent of disease in patients with recurrent MTC, although (18)F-FDG PET/CT may identify more lesions. However, (68)Ga-DOTATATE PET/CT can be a useful complementary imaging tool and may identify patients suitable for consideration of targeted radionuclide somatostatin analogue therapy.