Abstract
BACKGROUND: 6-[(18)F]fluoro-L-3,4-dihydroxyphenyl alanine ([(18)F]FDOPA) is a commonly used PET tracer for the detection and staging of neuroendocrine tumors. In neuroendocrine tumors, [(18)F]FDOPA is decarboxylated to [(18)F]dopamine via the enzyme amino acid decarboxylase (AADC), leading to increased uptake when there is increased AADC activity. Recently, in our hospital, a new GMP compliant multi-dose production of [(18)F]FDOPA has been developed, [(18)F]FDOPA-H, resulting in a higher activity yield, improved molar activity and a lower administered mass than the conventional method ([(18)F]FDOPA-L). AIMS: This study aimed to investigate whether the difference in molar activity affects the [(18)F]FDOPA uptake at physiological sites and in tumor lesions, in patients with NET. It was anticipated that the specific uptake of [(18)F]FDOPA-H would be equal to or higher than [(18)F]FDOPA-L. METHODS: We retrospectively analyzed 49 patients with pathologically confirmed NETs and stable disease who underwent PET scanning using both [(18)F]FDOPA-H and [(18)F]FDOPA-L within a time span of 5 years. A total of 98 [(18)F]FDOPA scans (49 [(18)F]FDOPA-L and 49 [(18)F]FDOPA-H with average molar activities of 8 and 107 GBq/mmol) were analyzed. The SUVmean was calculated for physiological organ uptake and SUVmax for tumor lesions in both groups for comparison, and separately in subjects with low tumor load (1-2 lesions) and higher tumor load (3-10 lesions). RESULTS: Comparable or slightly higher uptake was demonstrated in various physiological uptake sites in subjects scanned with [(18)F]FDOPA-H compared to [(18)F]FDOPA-L, with large overlap being present in the interquartile ranges. Tumor uptake was slightly higher in the [(18)F]FDOPA-H group with 3-10 lesion (SUVmax 6.83 vs. 5.19, p < 0.001). In the other groups, no significant differences were seen between H and L. CONCLUSION: [18F]FDOPA-H provides a higher activity yield, offering the possibility to scan more patients with one single production. Minor differences were observed in SUV's, with slight increases in uptake of [(18)F]FDOPA-H in comparison to [(18)F]FDOPA-L. This finding is not a concern for clinical practice, but could be of importance when quantifying follow-up scans while introducing new production methods with a higher molar activity of [(18)F]FDOPA.