Physiological uptake of 68Ga-DOTATOC in normal organs: influence of higher hormone levels.

Objectives PET/CT with 68Ga-DOTATOC has been used in patients with neuroendocrine tumors. It is known that physiological uptake can be seen in some organs, but whether elevated hormone levels can affect the physiological uptake of DOTATOC remains unknown. The purpose of this study was to investigate the influence of higher hormone levels for physiological uptake of 68Ga-DOTATOC.

Methods Among the patients who underwent DOTATOC-PET/CT scan between June 2011 and November 2014, there were 9 pts with higher ACTH, 32 pts with higher gastrin, 11 pts with higher insulin, 5 pts with higher glucagon, and 10 pts with higher FGF-23 values. Physiological uptake in pituitary gland, thyroid, pancreatic uncus and body, liver, spleen, adrenal glands, kidneys, and bowel were compared with that of 129 patients without any elevated hormone levels. Patients with several higher hormone levels at the same time were excluded in this study, and the initial scan was reviewed in patients who had multiple scans.

Results In pituitary gland, physiological uptake was lower in patients with higher ACTH (SUVmax±SD=6.1±4.8, p=0.029), and higher in patients with higher glucagon (11.6±2.6, p=0.025) than in normal subjects (8.4±3.3). In thyroid, that was higher in patients with higher insulin (2.8±0.8, p=0.014) and FGF-23 (3.3±0.8, p=0.001) levels than in normal subjects (2.3±0.8). In pancreatic uncinate process, that was lower in patients with higher ACTH (5.0±3.6, p=0.032) than in normal subjects (6.5±3.1). In adrenal glands, physiological uptake was lower in patients with higher ACTH (11.4±4.8, p=0.042), and higher in patients with higher glucagon levels (17.9±2.3, p=0.017) than in normal subjects (13.8±4.8). In kidneys, that was higher in patients with higher insulin (21.4±5.1, p=0.037) than in normal subjects (18.9±5.6). Finally, in bowel, that was higher in patients with a higher FGF-23 level (5.9±1.4, p=0.036) than in normal subjects (4.8±1.3). However, according to a multiple-comparison test (Steel's test), these differences did not reach statistical significance. In addition, no significant difference caused by higher hormone levels was observed in physiological uptake in pancreatic body portion, liver, and spleen.

Conclusions Our data suggest that some hormones, such as ACTH, can alter the physiological uptake of DOTATOC, which may indicate fluctuation of expression of somatostatin receptors.