Highly variable biodistribution of 68Ga labeled somatostatin analogues 68Ga-DOTA-NOC and 68Ga-DOTA-TATE in neuroendocrine tumors: clinical implications for somatostatin receptor directed PET/CT

Abstract

Background: Somatostatin receptor (SSTR)-targeted positron emission tomography/computed tomography (PET/CT) imaging has risen to the forefront for neuroendocrine tumor (NET) detection and management, yet the variability of significant uptake variability (SUV) as a semiquantitative measure of disease detection and tumor response to treatment has not been fully explored. Methods: We assess the reproducibility and interscan variability of SUV metrics of normal tissue and NET in serial 68Ga-DOTA-NOC and 68Ga-DOTA-TATE PET imaging to clinically monitor disease state. Eighty-one patients were enrolled in this retrospective study. Results: Both primary and metastatic hepatic lesions demonstrated SUV (SUVmean 16.5±8.0). The median SUVmean was 16 for the spleen, 9.7 for the pituitary, 12.6 for the adrenal glands, and 4.8 for the liver. The normal pituitary gland demonstrates focal homogenous uptake with SUVmax range of 4.5-23. The adrenal gland showed uptake with SUVmax range of 4.1-29.4, which is more than two times greater than liver uptake (SUVmean range, 2.3-12.4). Highest physiological uptake seen in the spleen (average SUVmean of 17.3, range of 5.4-34.4). Conclusions: The highly variable nature of regional SUVmean and SUVmax in both physiologic tissue and lesions suggests the need for incorporation of more reliable quantitative measures for clinical decision making.