Comparison of 201Tl solution sources in UK hospitals, 2001

During recent years, concerns have been raised within the nuclear medicine field about the accuracy of activity measurements for 201Tl. And indeed, NPL calibrations repeatedly indicated that the level of impurities present in such samples and the significant amount of activity adsorbed onto the glass wall of the container could produce erroneous results. In addition, the standard P6 vials, in which 201Tl solution had been previously supplied, were recently replaced with the new ''10R Type 1 plus'' Schott vials. To assess the magnitude of these effects on the accuracy of clinical measurements of the activity of 201Tl, an intercomparison exercise was conducted between the National Physical Laboratory (NPL), Nycomed-Amersham (NA) and the UK hospital physics community. The majority of the 273 reported results were within the ± 10 % limit of accuracy that hospitals aim to achieve for diagnosis, biased high. The tendency to overestimate the activity was more evident for syringe measurements. The exercise also revealed that the adsorption losses experienced with P6 vials had been solved by the introduction of the 10R vials, but individual calibrators need to be recalibrated for this new container. (author)