The contribution of combined imaging based on volumetric parameters with Ga-68 DOTA-TATE and F-18 FDG PET/CT in neuroendocrine tumors; comperative study with tumor proliferation indexes and serum chromogranin-A levels

Objectives To compare Ga-68 labeled somatostatin analogues and F-18 FDG uptake characteristics based on semi-quantitative and volumetric parameters and to investigate the relationship between activity involvements and Ki-67 and Cg-A levels in neuroendocrine tumors (NET).

Methods The 41 patients with NET were included to study (19 female, 22 male; age range 30-79; average age 56,7±12,3). All patients underwent somatostatin receptor imaging (SRI) with Ga-68 DOTA-TATE and F-18 FDG PET-CT. Somatostatin receptor expressions and metabolic activities of the lesions were calculated inside the region and volume of interest drawn around the tumor as standard uptake value (SUV), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) in FDG PET-CT, somatostatin receptor density (SRD) and total lesion somatostatin receptor expression (TLSRE) in SRI. Patients allocated as well (G1; Ki-67≤2), intermediate (G2; Ki-67:3-20) and poor differentiated (G3; Ki-67>20).

Results Of the total 41 patients, 22 were G1 (%53.7), 14 were G2 (%34.1), 5 were G3 (%12.2) NET. TLSRE values of liver metastases were significantly higher than TLG values (p<0.001). Positive correlations were found between Ki-67 levels and FDG SUV max (p=0.025, r=0,430), MTV (p=0.029, r=0,420) and TLG (p=0.004, r=0,537) of the primary tumor. A positive correlation existed between Cg-A and SRD (p<0.001, r=0.547), TLSRE (p<0.001, r=0.576), MTV (p=0.001, r=0.512) and TLG (p<0.001, r=0.544) of total tumor burden of the entire body.

Conclusions Due to different biological characteristics of the tumors, combination of SRI and F-18 FDG PET-CT studies will provide complementary information in NET’s. Volume-based parameters as characterized by SRD and TLSRE values can be used more safely in Ga-68 SRI for tumor burdens of lesions and whole-body.