The [ 68 Ga]Ga-DOTATATE and [ 18 F]FDG PET-CT imaging characteristics of metastatic neuroendocrine tumors

Introduction: The [ 68 Ga]Ga-DOTA-conjugated somatostatin receptor imaging (SR) is becoming the standard imaging procedure in the management of the neuroendocrine tumors (NET). Meanwhile [ 18 F]FDG PET-CT as an adjunctive tool provides useful information in the imaging of NETs. The aim of this study was to compare the diagnostic utility of these imaging methods as well as demonstrate uptake characteristics of NETs. Methods: 41 patients (17 M, 21 F; mean: 57.1 years old) with the diagnosis of metastatic neuroendocrine tumors were included in the study. [ 18 F]FDG PET-CT and/or [ 68 Ga]Ga-DOTATATE PET-CT imaging was performed in patients for initial staging, restaging, treatment response evaluation, lesion characterization or to find an unknown primary tumor. The results of the patients were compared with oncologic follow up results and/or pathology results. Results: The size of the lesions were mean: 34 mm and the standardized uptake value in [ 18 F]FDG PET/CT SUVmax(F) and SUV in [ 68 Ga]Ga-DOTATATE PET/CT SUVmax(G) of the lesions were mean: 10.6 and 32.4 respectively. According to the follow up results of the 23 patients with available initial and follow up imaging studies, the management of seven patients were changed (30%). Among the NET group grade 1-3 tumors SUVmax(F) and SUVmax(G) levels were not significantly different. Conclusion: Diagnostic workup of metastatic NET's should include either or both of the [ 68 Ga] DOTATATE and [ 18 F]FDG PET-CT imaging studies. Individualization of the imaging method of choice in every single patient would be an appropriate approach.