SU-GG-T-49: Improved Technique for Determining Y-90 Glass Microsphere Activity Delivered

Abstract

Purpose: Radioembolization of hepatic metastases with 90 Y microspheres requires that the user can accurately measure the source activity and consistently determine the completion of dose delivery. To determine the most effective technique for determining the completion of a single dose application, we have retrospectively examined dose rate measurements and source vial assays from 263 radioembolizations using Y‐90 glass microspheres. Method and Materials: Y‐90 glass microspheres were measured in an Atomlab 100 dose calibrator. Unit doses were supplied in 0.6 mL of sterile water contained in a v‐bottom vial secured within a 12 mm clear acrylic vial shield. Assays were obtained for the point source configuration (microspheres concentrated into the 0.3 ml v‐bottom) and for a distributed source configuration (microspheres distributed in 0.6 ml). Assayed values were compared to the nominal activity. Source dose rates were measured using Inovision 451P. Manufacturer's recommended measurements were followed. In addition, the beta dose rate from the top of the unshielded source vial was measured using Thermo Eberline RO7BM ionization chamber. Initial and final dose rate measurements were compared to the measured residual activity. Results: The axial dependence of the dose calibrators ranged from 0 to 5%. Measured activity in the point source configuration was on average 94.5% of the decayed calibrated activity (R2=0.996). However, measured activity in the distributed source configuration was on average 84.5% of the decayed calibrated activity (R2=0.998). Residual activity as a function of the beta specific dose rate measurements was linear (r2 = 0.4). Conclusion: This study has shown that using a point source configuration for source vial assays and using the beta specific dose rate measurements to accurately determine dose delivery does provide a more consistent and accurate determination of yttrium‐90 glass microsphere activity delivery and improve radioembolization quality assurance. Riad Salem, MD consultant for MDS‐Nordion.