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

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 Y activity in vials with quantitative Y PET/CT assessment of the same vials. We compared Y PET-measured activity (A) for 56 Y-labeled glass and 18 Y-labeled resin microsphere vials with the calibrated activity specified by the manufacturer (A). Additionally, the same analysis was performed for 4 Y-chloride vials. The mean A/A 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/A ratio for Y-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.