Abstract
1143
Objectives: Since the development of somatostatin receptor radiopharmaceuticals for detection of neuroendocrine tumors using positron emission tomography (PET), there have been multiple studies defining the range of uptake in normal organs to include the pituitary gland. However, the biodistribution and maximum standardized uptake value (SUVmax) described in the literature for Ga-68 DOTATATE PET have been derived from images using standard iterative reconstruction and non time-of-flight (TOF) PET scanners. Little data has been reported on the normal range of uptake of DOTATATE PET using time of flight (TOF) images, which may yield higher SUVmax measurements, especially for small structures such as the pituitary due to greater spatial resolution and reduced partial volume effect. The objective of this educational exhibit is to: 1) discuss the normal range of SUVmax for pituitary on DOTATATE imaging using TOF PET, and 2) discuss the relationship between SUVmax and pituitary tumors.
Methods: A recent DOTATATE PET study at our institution demonstrated high uptake in the pituitary with SUVmax greater than SUVmax in the spleen (34.6 vs. 28.4). The study was performed on a Siemens Biograph mCT scanner with TOF. This prompted a retrospective review of 10 DOTATATE studies performed on the same scanner. The SUVmax of the pituitary was measured in each study. Also, a review of the current literature was undertaken to determine the range of normal values for SUVmax in the pituitary on DOTATATE scans and the relationship between DOTATATE uptake and primary pituitary tumors.
Results: The mean value for the pituitary SUVmax on our TOF scanner was 22.8 (range 13.8 to 40.2), whereas published data demonstrate mean values for normal pituitary SUVmax ranging from 7.6 to 11 as measured on non-TOF PET scanners. Also, prior studies examining tumor uptake from microadenomas demonstrate relatively decreased uptake compared to normal pituitary. Increased uptake in an anatomically normal sella was not associated with pathology. This is likely due to the variation in expression of somatostatin (SST) subtypes that can be found in adenomas, namely subtype 1, 2, 3 and 5. DOTATATE primarily binds subtype 2 SST receptors, which can explain why primary pituitary lesions may bind DOTATATE yet show decreased DOTATATE concentration relative to normal pituitary. However, DOTATATE avidity in an overt sellar lesion may represent pituitary macroadenoma, pituitary carcinoma or meningioma.
Conclusions: Normal pituitary SUVmax can be markedly increased on TOF DOTATATE PET imaging compared to previously reported normal ranges derived from non-TOF PET scanners. Furthermore, pituitary microadenomas are not associated with increased, but rather decreased DOTATATE uptake compared to normal pituitary. Additional imaging to investigate high DOTATATE activity in an anatomically normal sella is likely unwarranted.