Journal article
SIR-Spheres activity measurements reveal systematic miscalibration
The Journal of nuclear medicine (1978), Vol.63(8), pp.1131-1135
01/06/2022
DOI: 10.2967/jnumed.121.262650
PMID: 34992155
Abstract
Accurate dosimetry-guided radiopharmaceutical therapy fundamentally relies on knowledge of the quantity of radioactivity administered to patients. The purpose of this work was to perform an independent and NIST-traceable activity measurement of
Y SIR-Spheres®.
Gamma spectroscopic measurements of the
Y internal pair production decay mode were made using a high-purity germanium detector. Un-modified patient SIR-Spheres® vials were placed within a high-density polyethylene source holder positioned at a distance of 210 cm from the detector, with acquisition durations of 3 - 6 hours. 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 two independent and NIST-traceable methods. Resulting
Y activity measurements were compared against the manufacturer activity calibration.
Measured SIR-Sphere® vials (
= 5) were found to contain 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 two distinct efficiency calibration methods were found to agree within 1%. Uncertainty in individual measurements was dominated by counting statistical uncertainty (~2.5%), uncertainty in the internal pair production branching ratio of
Y (1.5%), and efficiency calibration (1.2% - 1.9%).
The primary SIR-Spheres® activity calibration appears to be a significant underestimate of true activity. This mis-calibration has likely been consistent for as long as the SIR-Sphere® product has been available. This finding should be independently verified, and steps should be taken by the manufacturer to establish an accurate and traceable activity standard.
Details
- Title: Subtitle
- SIR-Spheres activity measurements reveal systematic miscalibration
- Creators
- Stephen A Graves - University of IowaMolly Martin - University of IowaAshok Tiwari - University of IowaMichael J Merrick - University of IowaJohn J Sunderland - University of Iowa
- Resource Type
- Journal article
- Publication Details
- The Journal of nuclear medicine (1978), Vol.63(8), pp.1131-1135
- DOI
- 10.2967/jnumed.121.262650
- PMID
- 34992155
- NLM abbreviation
- J Nucl Med
- ISSN
- 0161-5505
- eISSN
- 1535-5667
- Language
- English
- Date published
- 01/06/2022
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering; Radiology; Physics and Astronomy; Radiation Oncology; Pharmacy Practice and Science
- Record Identifier
- 9984312972202771
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