ACCURACY OF DOSE CALIBRATORS FOR GALLIUM-68 PET IMAGING: UNEXPECTED FINDINGS IN A MULTI-CENTRE CLINICAL PRE-TRIAL ASSESSMENT.

Abstract

AIMS: We report the discovery of a systematic miscalibration during the work-up process for site validation of a multi-centre clinical PET imaging trial using68Ga, which manifested as a consistent and reproducible underestimation in the quantitative accuracy (assessed by SUV) of a range of PET cameras from different manufacturers at a number of different facilities around Australia.METHODS:Sites were asked to follow a strict preparation protocol to create a radioactive phantom with68Ga to be imaged using a standard clinical protocol prior to commencing imaging in the trial. All sites had routinely used68Ga for clinical PET imaging for many years. The reconstructed image data were transferred to an imaging core laboratory for analysis, along with information about ancillary equipment such as the radionuclide dose calibrator. Fourteen PET systems were assessed from ten nuclear medicine facilities in Australia with the aim for each PET camera being to produce images within ±5% of the true SUV value.RESULTS:At initial testing, 10 of the 14 PET systems underestimated the SUV by 15% on average (range -13% - -23%). Multiple PET cameras at one site, from two different manufacturers, were all similarly affected, suggesting a common cause. We eventually identified an incorrect factory-shipped dose calibrator setting from a single manufacturer as being the cause. The calibrator setting for68Ga was subsequently adjusted by the users so that the reconstructed images produced accurate values.CONCLUSION:PET imaging involves a chain of measurements and calibrations to produce accurate quantitative performance. Testing of the entire chain can, however, be simply performed and should form part of any quality assurance (QA) programme or pre-qualifying site assessment prior to commencing a quantitative imaging trial or clinical imaging.