Focal uptake of 68Ga-DOTATOC in the pancreas: pathological or physiological correlate in patients with neuroendocrine tumours?

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Abstract

Purpose

Neuroendocrine tumours are frequently located in the upper abdomen and especially in the pancreas. Imaging of the abdomen with somatostatin analogs such as 68Ga-DOTA-Phe1-Tyr3-octreotide (DOTATOC) is a standard approach for imaging neuroendocrine cancer, but is still challenging due to physiological and technical considerations in this area. Therefore, the aim of this study was to further investigate the origin of 68Ga-DOTATOC findings in the pancreas.

Methods

Forty-three consecutive patients with neuroendocrine tumours were examined by 68Ga-DOTATOC positron emission tomography (PET)/CT for staging or restaging. As imaging of the upper abdomen is frequently affected by breathing artefacts, PET and CT data were analysed for misalignment and rearranged if necessary. Any noticeable uptake in the pancreas was described. Tracer uptake in the head of the pancreas and the liver was measured by means of maximum and average standard uptake value (SUVmax, SUVav). The reference standards (malignant versus benign) for correlation with PET findings were clinical and radiological follow-up (mean follow-up time 14 months) (n = 37) or histological confirmation (n = 6).

Results

In 23 of 43 studies (54%) misalignment between PET and CT data was found with a mean value of 1.4 cm. Visual assessment demonstrated that 20 of 43 scans (46.6%) showed no uptake in the head of the pancreas. Of 43 scans, 23 (53.4%) showed noticeable uptake with focal pattern in the head of the pancreas in 10 scans and irregular pattern in 13 scans. Follow-up indicated malignant pancreatic lesions in three patients. The pancreatic head to liver SUVav ratios in these patients ranged from 1.62 to 6.85, whereas in cases of uptake without known malignancy ratios ranged from 0.56 to 1.19. Considering SUVmax, the ratio ranged from 3.24 to 9.1 and from 0.84 to 1.47, respectively. No statistically significant difference was noted between uptake in the head of the pancreas and the liver in patients without malignant pancreatic tumours (p > 0.05).

Conclusion

68Ga-DOTATOC uptake in the head of the pancreas is a common finding in patients undergoing 68Ga-DOTATOC PET/CT. However, this finding most likely represents a physiological condition, especially if the uptake in the pancreatic head is similar to the uptake in the liver (uptake ratio head to liver SUVav < 1.4). Therefore, quantification is recommended to avoid false-positive diagnosis. Misalignment due to respiratory motion must always be taken into account.