Combined imaging with 68Ga-DOTA-TATE and 18F-FDG PET/CT on the basis of volumetric parameters in neuroendocrine tumors

Aim To assess the additional contribution of the combined imaging approach with 68Ga-DOTA-TATE and fluorine-18 fluorodeoxyglucose (18F-FDG) on the basis of volumetric parameters in neuroendocrine tumors (NETs). Materials and methods Forty-one patients with NET (19 women, 22 men; age range: 30–79 years; mean age: 56.7±12.3 years) underwent 68Ga DOTA-TATE and 18F-FDG PET/computed tomography (CT) imaging. Within the drawn regions of interest, in addition to evaluating the maximum and mean standardized uptake values (SUVmax and SUVmean), the metabolic tumor volume (MTV) and total lesion glycolysis (TLG) in 18F-FDG PET/CT imaging, and the somatostatin receptor density and total lesion somatostatin receptor expression (TLSRE) in 68Ga somatostatin receptor imaging (SRI) were measured. The patients were graded on the basis of the proliferation index: well (G1; Ki-67 ≤2), moderately (G2; Ki-67=3–20), and poorly (G3; Ki-67>20) differentiated groups. Results Of the 41 NET patients, 22, 14, and five were in the G1 (53.7%), G2 (34.1%), and G3 (12.2%) groups, respectively. Liver metastases had significantly higher TLSRE values than the TLG values. Ki-67 levels showed a positive correlation with the primary tumor MTV and TLG values. Cg-A levels had a positive correlation with the volumetric parameters of the whole-body tumor burden (P<0.001). Conclusion 68Ga SRI and 18F-FDG PET/CT provide complementary information on treatment protocol and response assessment. While assessing the prognosis and tumor aggressiveness, lesions and whole-body tumor burdens can be calculated on the basis of volumetric parameters by 18F-FDG PET/CT using MTV and TLG, and by 68Ga SRI using somatostatin receptor density and TLSRE.