Detection of Bone Metastases by (68)Ga-DOTA-SSAs and (18)F-FDG PET/CT: A Two-Center Head-to-Head Study of Gastroenteropancreatic Neuroendocrine Neoplasms

PURPOSE: This study aimed to assess the efficacy of dual-tracer [(68)Ga-DOTA-somatostatin receptor analogs (SSAs) and (18)F-fluorodeoxyglucose (FDG)] positron emission tomography/computed tomography (PET/CT) imaging for detecting bone metastases (BMs) in patients with gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs). METHODS: We retrospectively enrolled 74 GEP-NEN patients with BMs from two centers, who underwent dual-tracer PET/CT from January 2014 to March 2021. We compared and analyzed effectiveness of the dual PET/CT imaging techniques on the BMs, based on (18)F-FDG and (68)Ga-DOTA-SSAs. Specifically, we analyzed the imaging results using χ(2) tests for classification variables, paired-sample tests for number of BMs, Wilcoxon's signed rank test for number of lesions, and the Kruskal–Wallis test for standard uptake value (SUV) ratio comparison. The correlation of dual-tracer SUVmax with Ki-67 index was analyzed by Spearman's correlation coefficient. RESULTS: The detection efficiencies of dual-tracer PET/CT imaging in patients with different pathologies showed discordant for detecting liver metastases and BMs in group neuroendocrine tumor (NET) G3, (68)Ga-DOTA-SSAs was better at detecting BMs for NET G3 (P=0.049 for SUV(T/B) and P=0.026 for the number of metastatic lesions). In addition, statistical significance was found among osteogenesis group, osteolysis group, and the no-change group (for bone SUV(T/B) value detected by (18)F-FDG and Ki-67 index, osteogenesis group < osteolysis group; for bone SUV(T/B) detected by (68)Ga-DOTA-SSAs, osteogenesis group > the no-change group). What is more, liver and bone SUVmax and Ki-67 index were positively correlated in (18)F-FDG imaging (P < 0.001 for liver; P=0.002 for bone), and negatively correlated in (68)Ga-DOTA-SSAs imaging (P < 0.001 for liver; P=0.039 for bone). CONCLUSIONS: (68)Ga-DOTA-SSAs was superior to (18)F-FDG for detecting BMs in NET G1/G2 (well and moderately differentiated NETs), as well as in NET G3 (poorly differentiated NETs). Relatively good differentiation was observed in the osteogenesis group. In addition, dual-tracer PET/CT imaging results were observably correlated with tumor differentiation.