Physiological uptake of 68Ga-DOTA-NOC in the head of the pancreas in patients with NET

Objectives Our aim was to study the incidence of increased uptake of 68Ga-DOTA-NOC in the head of the pancreas and to evaluate possible causes for such bio-distribution of the tracer.

Methods We retrospectively reviewed 214 scans in 88 patients with NET not involving pancreas. Scans were performed 50-70 minutes after administration of 1,5 - 2,0 MBq/Kg of 68Ga-DOTA-NOC. In order to evaluate the variation of uptake within the same patients, we included only patients with multiple scans over time (2-6 scans with an elapsed time of 3-36 months). The uptake in the head of the pancreas was measured using SUVmax and compared with normal liver parenchyma (Target/Liver ratio).

Results Increased uptake could be classified in two patterns: diffuse and focal. Diffuse pattern was identified as diffuse uptake in the head of the pancreas proximal to the duodenum; focal pattern was a smaller area of intense uptake mainly in the inferior aspect of the head. Increased uptake was observed in 69/214 scans; the incidence of diffuse and focal patterns were 26% and 5% respectively. On a patient basis, increased uptake was found in 31/88 patients: stable focal uptake in 6 pts (7%), stable diffuse pattern in 16 pts (18%), while 9 pts (10%) with diffuse uptake were negative at a subsequent scans. Overall in 79/88 pts (89%) the presence or absence of increased uptake was stable over time. Patients with diffuse pattern showed SUVmax close to the liver (mean 5±1,6; Liver 6,3±2,1; Target/liver ratio= 0,8), while the focal pattern showed an higher uptake (mean 12,6±2,2; Liver 6,4±1,5; Target/liver ratio=1,9).

Conclusions The stability of uptake in the large majority of patients suggests that the main reason for increase uptake may be histo-anatomical. The diffuse pattern is more frequent and relatively easy to identify, while the presence of focal pattern is less common and could affect the interpretation of the scan