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

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 (68)Ga-DOTA-NOC and (68)Ga-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 (SUV(mean) 16.5±8.0). The median SUV(mean) 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 SUV(max) range of 4.5–23. The adrenal gland showed uptake with SUV(max) range of 4.1–29.4, which is more than two times greater than liver uptake (SUV(mean) range, 2.3–12.4). Highest physiological uptake seen in the spleen (average SUV(mean) of 17.3, range of 5.4–34.4). CONCLUSIONS: The highly variable nature of regional SUV(mean) and SUV(max) in both physiologic tissue and lesions suggests the need for incorporation of more reliable quantitative measures for clinical decision making.