SIR-Spheres Activity Measurements Reveal Systematic Miscalibration.

Graves, Stephen A; Martin, Molly; Tiwari, Ashok; Merrick, Michael; Sunderland, John · J Nucl Med · 2022

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Abstract

The purpose of this work was to perform an independent and National Institute of Standards and Technology-traceable activity measurement of <sup>90</sup>Y SIR-Spheres (Sirtex). γ-spectroscopic measurements of the <sup>90</sup>Y internal pair production decay mode were made using a high-purity germanium detector. <b>Methods:</b> Measured annihilation radiation detection rates were corrected for radioactive decay during acquisition, dead time, source attenuation, and source geometry effects. Detection efficiency was determined by 2 independent and National Institute of Standards and Technology-traceable methods. <b>Results:</b> Measured SIR-Spheres vials (<i>n</i> = 5) contained more activity than specified by the manufacturer calibration; on average, the ratio of measured activity to calibrated was 1.233 ± 0.030. Activity measurements made using 2 distinct efficiency calibration methods agreed within 1%. <b>Conclusion:</b> The primary SIR-Spheres activity calibration appears to be a significant underestimate of true activity.

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