Semiquantitative analysis of physiological biodistribution of 68GA-dotatate and 68GA-dotanoc

An important common feature of neuroendocrine tumors (NETs) is overexpression of somatostatin receptors (SSTR). Up to now, five different SSTR (SSTR1-5) subtypes have been identified. 68Ga-DOTATATE ve 68Ga-DOTANOC are commonly used agents in NET imaging. While 68Ga-DOTATATE shows a spesific high binding affiniy for SSTR2, 68Ga-DOTANOC has a broader SSTR subtype affinity including SSTR2, SSTR3 and SST5. SSTRs not only are confined to NETs, but also are present in a whole range of normal tissues and organs that include the pituitary, the adrenals and the kidneys. Although there has an increasing number of published data which demonstrate the superior role of 68Ga-DOTATATE and 68Ga-DOTANOC in the staging and management of NETs, little is known about the characteristics of biodistribution in the sites of physilogical uptake. In this sudy, we aimed 1)To map the normal distribution pattern of 68Ga-DOTATATE and 68Ga-DOTANOC by using SUVmax and SUVmean (±SD) parameters, 2)To define a normal distribution range (min-max), 3)To evaluate the relationship between the uptake patterns and the imaging intervals and finally 5)To compare the data with the current literature. Forty patients (23 females, 17 males, mean age 52,50±15,82 years) referred to our department for 68Ga-DOTATATE and 68Ga-DOTANOC PET/CT imaging were included in the study. Twenty five of 40 patients had undergone 68Ga-DOTATATE PET/CT imaging, the remaining 15 patients had undergone 68Ga-DOTANOC PET/CT imaging. In our study, uptake in the spleen, adrenals, pancreatic head, palatine tonsil and breast tissue showed no significantly important difference for SUVmax and SUVmean values between two groups. In the lymph nodes, while SUVmean values were similar for two groups, SUVmax values were detected to be significantly higher in 68Ga-DOTATATE group. We could not perform statistical analysis for prostate and thymus because of the few number of patients. The remaining whole organs showed significantly higher SUVmax and SUVmean values in 68Ga-DOTATATE group than 68Ga-DOTANOC group. Also, we analysed the local distribution patern for pancreas (head-body-tail) and stomach (fundus-other regions). For both agents, significantly higher uptake was detected in the fundus than other regions of the stomach and also in the pancreatic head than body and tail of the pancreas. We also evaluated the difference in the uptake of right and left adrenals and small and large bowel, and no statistically important difference was detected. We also analysed the relationship between imaging intervals (>60 ve ?60 minutes) and uptake patterns for each group. Only in the 68Ga-DOTANOC group, palatine tonsil and fundus of the stomach showed higher SUVmean values when the imaging protocol was started after 60 minutes. Except these, no significantly important difference for SUVmax and SUVmean values were detected between two groups. When compared with the current literature, we found significantly higher uptake values for the pituitary, the spleen and the liver for both 68Ga-DOTATATE and 68Ga-DOTANOC. For pancreatic head, our data was higher for some of the literature values while for some it was similar. We also found similar uptake values with the literature for parotid gland, lung, kidney, adrenals, pancreatic body, large bowel, muscle and bone marrow for both agents. 68Ga-DOTATATE and 68Ga-DOTANOC PET/CT are emerging as a standard approach for imaging NET; however there are still diagnostic challenges because of physiological uptake at several organ sites. Although there has been an increasing number of published data which demonstrate the superior role of 68Ga-DOTATATE and 68Ga-DOTANOC in the staging and management of NETs, little is known about the characteristics of biodistribution in the sites of physiological uptake. Our study is the only one in the literature comparing the biodistribution of 68Ga-DOTATATE and 68Ga-DOTANOC in a large number of organ sites. Kabasakal et al. has compared the biodistribution of 68Ga-DOTATATE and 68Ga-DOTANOC in the same group of patients, especially at the tumoral sites and a few physiological sites such as pituitary, adrenal, liver, spleen and salivary glands. In conclusion, our study demonstrated the biodistribution of 68Ga-DOTATATE and 68Ga-DOTANOC in normal organs using SUVmax and SUVmean values semiquantitatively and outlines the range of SUVmax and SUVmean for various organs. Knowledge of normal biodistribution pattern and SUV values may contribute to the interpretation of this imaging and to differentiation of physiological and pathological patterns