A multicenter study on observed discrepancies between vendor-stated and PET measured 90 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 administrated activity. This multi-center (n center =4), multi-device (n PET =5) study compared the manufacturer-declared 90 Y activity in vials with quantitative 90 Y PET/CT-assessment of the same vials. We compared 90 Y PET-measured activity (A PET ) for 90 Y-labeled glass (n g =56) and resin (n r =18) microsphere vials with the calibrated activity specified by the manufacturer (A M ). Additionally, the same analysis was performed for 90 Y-chloride vials (n cl =4). The mean A PET /A M ratio for glass microspheres was 0.79±0.04 [range: 0.71-0.89] and for resin microspheres was 1.15±0.06 [range: 1.05-1.25]. Mean A PET /A M ratio for 90 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 while a close agreement was found for chloride solutions. We expect the reported discrepancies will promote further investigations to establish reliable and accurate patient dosimetry and dose-effect assessments.