A Multicenter Study on Observed Discrepancies Between Vendor-Stated and PET-Measured ⁹⁰Y Activities for Both Glass...

Dosimetry-guided treatment planning in selective internal radiation therapy relies on accurate and reproducible measurement of administered activity. This 4-center, 5-PET-device study compared the manufacturer-declared ⁹⁰Y activity in vials with quantitative ⁹⁰Y PET/CT assessment of the same vials. We compared ⁹⁰Y PET-measured activity (A_PET) for 56 ⁹⁰Y-labeled glass and 18 ⁹⁰Y-labeled resin microsphere vials with the calibrated activity specified by the manufacturer (A_M). Additionally, the same analysis was performed for 4 ⁹⁰Y-chloride vials. The mean A_PET/A_M ratio was 0.79 ± 0.04 (range, 0.71-0.89) for glass microspheres and 1.15 ± 0.06 (range, 1.05-1.25) for resin microspheres. The mean A_PET/A_M ratio for ⁹⁰Y-chloride vials was 1.00 ± 0.04 (range, 0.96-1.06). Thus, we found an average difference of 46% between glass and resin microsphere activity calibrations, whereas close agreement was found for chloride solutions. We expect that the reported discrepancies will promote further investigations to establish reliable and accurate patient dosimetry and dose-effect assessments.