Determination of volume-specific correction factors and geometry effects of 90Y activity measurement in dose calibrators

Background: Yttrium-90 (90Y) is widely used in nuclear medicine for therapeutic purposes. The radiation dose of radiopharmaceuticals relates to the activity of the radionuclide which is measured in the dose calibrator during radiopharmaceutical preparations. Objectives: The objectives of this study were to determine volume-specific correction factors and investigate the geometry effects of 90Y activity measurement in dose calibrators. Materials and methods: Four dose calibrators from two institutes were independently measured. The 3-mL plastic syringe and the 10-mL glass vial were used to investigate the geometry effects using the initial calibration factors for each dose calibrator. The comparison between actual activity and measured activity was expressed as the percentage errors. For volume-specific correction factor, the value for each volume was calculated based on the actual and measured activity at 0.5, 1.0, 1.5, 2.0 and 2.5 mL. Results: Percentage error showed that 90Y activity measured in the 3-mL plastic syringe and the 10-mL glass vial were inaccurate. The activity measurements in the 3-mL plastic syringe were more accurate than in the 10-mL glass vial at all volumes for both containers in all dose calibrators. Our findings showed that increasing the volume of 90Y could result in underestimate of the measured activity. The maximum volume dependence in the 10-mL glass vial was about 20%. Hence, the volume-specific correction factors were determined for the 3-mL plastic syringe and the 10-mL glass vial for all dose calibrators. Conclusion: The geometry effect could impact the 90Y activity measurement on the dose calibrators. Using the volume-specific correction factor for each geometry of 90Y to compensate for the geometry effect could improve the accuracy of 90Y activity measurement. However, the volume-specific correction factors are depended on the dose calibrators. Therefore, the institutes need to establish their own volumespecific correction factors for 90Y activity measurement.