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