Objective: PET/CT imaging with 68Ga-1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid-D-Phe1-Tyr3-octreotide (DOTATOC) is useful in patients with neuroendocrine tumors (NETs). Functioning NETs by definition secrete abnormal levels of hormones, causing clinical symptoms. It is known that physiologic accumulation can be seen in some organs, but it remains unknown whether elevated hormone levels can affect the physiologic accumulation pattern of 68Ga-DOTATOC. We aimed to investigate the influence of higher hormone levels on physiologic accumulation of 68Ga-DOTATOC.
Methods: A total of 167 patients with known or suspected NET lesions were enrolled in this study. The numbers of patients with elevations of ACTH, gastrin, insulin, and no elevation were 10, 25, 7, and 125, respectively. We compared the maximum standardized uptake value (SUVmax) in various organs of each group.
Results: In the group with elevated ACTH levels, SUVmax in the pituitary gland, the uncinate process of the pancreas and adrenal glands was lower than those in the group with no elevation (5.7 ± 1.9 vs. 8.4 ± 3.1, P = 0.015; 4.7 ± 3.5 vs. 6.4 ± 2.8, P = 0.037; 10.8 ± 4.8 vs. 13.9 ± 4.7, P = 0.020, respectively). There were no differences in physiologic uptake of 68Ga-DOTATOC in the thyroid gland, the pancreatic body, the liver, the spleen, the bowel, or the kidney.
Conclusions: In NET patients with elevated ACTH levels, physiologic uptake of 68Ga-DOTATOC in the pituitary gland, the uncinate process of the pancreas and adrenal glands was significantly decreased. Other organs were unaffected.
Keywords: 68Ga-DOTATOC; ACTH; Physiologic accumulation; Pituitary gland; SUVmax.