Multicenter study of quantitative PET system harmonization using NIST-traceable 68Ge/68Ga cross-calibration kit

Purpose: The present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable Ge-68/Ga-68 source as the reference standard. Methods: We used Ge-68/Ga-68 dose calibrator and PET sources made with same batch of Ge-68/Ga-68 embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable Ge-68/Ga-68 sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site. Results: The average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was - 4.94% and - 12.22%, respectively, before, and - 0.14% and - 4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by - 4.70% under optimal conditions. Conclusion: Our proposed method using an NIST-traceable 68Ge/68Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies.