Radionuclide calibrator intercomparison study of clinical PET centres in England to a single traceable 68Ge syringe source.

OBJECTIVES The aim of this study was to characterize national variation in radionuclide calibrator activity response to a single National Institute of Standards and Technology (NIST) traceable reference ⁶⁸Ge source used as a surrogate for ¹⁸F at clinical PET centres in England using National Physical Laboratory approved techniques. METHODS Readings from 20 instruments at 13 centres using local ¹⁸F and ⁶⁸Ge factor settings were recorded with the source located in vial and syringe positions. Ten repeat measurements were conducted to investigate repeatability using % coefficient of variability (COV). Comparison ratios to investigate accuracy were made between calibrator responses and decay-corrected NISTref reference activity for syringe and vial position measurements. RESULTS The maximum %COV was 0.79%, while 90, 95 and 80% of calibrators conformed to 5% accuracy for ¹⁸F syringe, ⁶⁸Ge syringe and ⁶⁸Ge vial position readings, respectively. We revealed a trend towards reduced bias in measurements using Veenstra devices for ¹⁸F and using Capintec devices for ⁶⁸Ge factor settings. CONCLUSIONS This study demonstrated good repeatability in local device measurements. In total, 70% of English calibrators tested and 88% of all measurements performed achieved 5% accuracy. While statistically significantly bias was exhibited between different vendor equipment dependent upon radioisotope selected, our study recommends regular traceability checks for optimum instrument performance conducted within National Metrology Institutes guidelines.