Factors affecting the specific activity of [18F]fluoride from a [18O]water target.

Aim: Characterisation of the influence of different polymeric tube materials of a water target system, used for the production of 18F activity, on the specific activity of radiotracers. Material, methods: Target water samples taken from different locations of the 18F water target system of a Cyclone® 18/9 cyclotron, equipped with Teflon® (PTFE) or polypropylene (PP) tubes, were analyzed for non-radioactive [19F]fluoride content. [19F]Fluoride content was measured by ion chromatography (IC20, Dinoex) with suppressed conductivity detection. Both the ion chromatographic results and the amount of 18F activity produced were used for the calculation of the specific activity (SA) of [18F]fluoride at the start of the labelling synthesis. To check these results, the SA of the labelled receptor ligand [18F]ZK811460 was also determined by using the different tubing materials. Results: Dose-exposed PTFE tubes of the target dispensing (loading) system were identified to be a major source of [19F]fluoride contamination. Conclusion: By replacing PTFE tubes of the target dispensing system with PP tubes, the content of 19F was reduced considerably resulting in an increase of SA of the radiotracer [18F]ZK811460 by factor of two.