Biodistribution of the Ga-68 labeled somatostatin analogue DOTA-NOC in patients with neuroendocrine tumors: Characterization of uptake in normal organs and tumor lesions

Aim. The aim of the study was 1) to determine the normal biodistribution of radiolabeled somatostatin analogue ⁶⁸Ga DOTA-NOC; 2) to establish the range of its uptake in liver, bone and lymph node metastases in patients with NET, 3) to establish the cut-off value for differentiating between physiological uptake and tumor related sstr expression in the processus uncinatus of pancreas. Methods. Maximum standardized uptake values (SUV _max) of ⁶⁸Ga DOTA-NOC were determined in normal organs of 89 NET patients undergoing receptor PET/CT. In addition, SUV_max of primary pancreatic neuroendocrine tumors (pNET), liver, bone and lymph node metastases were evaluated. Results. SUV_max (mean±standard deviation) were determined in: pituitary gland 2.6±1.3, thyroid: 3.4±1.4, lung: 0.9±0.8, normal liven 6.9±2, spleen: 22.0±10.0, adrenal 6.0±2.5, kidney: 12.9±3.8, gastrointestinal tract 2.3±1.0, gluteal muscle:1.0±0.3, femur 0.8±0.3, blood pool 2.6± 1.2 and processus uncinatus of pancreas 5•8±2.0. SUV_max of ⁶⁸Ga DOTA-NOC was 19.6±13.4 (N.=200) in liver metastases, 12.5±10 (N.=67) in lymph nodes metastasis, 9.5±6.0 (N.=78) in bone lesions, and 20.8±10.8 (N.=26) in pancreatic neuroendocrine primary tumors. Target to non target (T/NT) ratios were 3.4±2.3 for liver metastases (with normal liver as non target organ), 14.5±19•1 for lymph node and 11.3±8.9 for bone metastases. Conclusion. There is a broad range of sstr expression in metastastic lesions and in pNET. The splenic uptake of ⁶⁸Ga DOTA-NOC is highly variable. ⁶⁸Ga DOTA-NOC is an excellent tracer for imaging somatostatin receptor positive tumors, which, due to the high target to non-target ratios, allows the detection of very small lesions, especially of lymph node and bone metastases.