Speaker
Description
Calibration of detector systems, traceable to the International System of Units (SI), is at the heart of any reliable measurement. For Nuclear Medicine applications, the knowledge of the amount of substance available in diagnostic or therapeutic radiopharmaceuticals can have a direct effect on patient outcomes. The National Research Council (NRC) of Canada is Canada’s National Metrological Institute and is charged with developing, maintaining and disseminating Canada’s standards for radioactivity. This work will describe the dissemination of three radionuclides standards: 99Mo, 177Lu and 90Y, in 2020 and 2021. Due to the short-lived nature of many radionuclides used in nuclear medicine, the standards for many -emitting isotopes are disseminated through the use of the NRC Secondary Standard of Ionizing Radiation Chamber System (SSIRCS)[1]. This is a collection of
Ionization Chambers (IC) which have been calibrated using artifacts standardized by primary methods directly traceable to the SI.
The SSIRCS has been calibrated for many radionuclides in two primary calibration
geometries; a 5ml serum vial and a 5ml flame sealed ampoule. If the calibration of the requested isotope has already been established, a standard can quickly be prepared by the end user or by the NRC and then exchanged. Measurements in the remote detection system (e.g. IC or -spectrometer system) and the SSIRCS provide all the necessary information to the end user to calibrate their detectors. This was how a recent (2021) standard for 99Mo was carried out.
The request for a traceable standard of 177Lu required more work because the end-user geometry was not a standard geometry maintained by NRC. Moreover, at the time of the request, the SSIRCS had not been calibrated for this isotope. In this case, the end user sent a dose of the 177Lu radioisotope in their calibration geometry to NRC. The dissemination of the standard was performed by certifying the activity concentration of the master volume provided to the NRC.
Calibration geometries are central to the dissemination of the standards. Occasionally, a geometry can be rather unique, as in the case of a glass sphere 90Y product that required standardization. The approach taken here was to prepare a mock artifact with cold glass spheres surrounded by a standardized 90Y solution.
The standard uncertainty with which standards of 99Mo, 177Lu and 90Y were provided by NRC were 1%, 0.5% and 0.3% respectively. Since the method by which this standard is disseminated varies according to the requirements of the end user, NRC has developed a range of techniques to address common nuclear medical isotopes.
References
[1] Galea R and Gameil K., Appl Radiat Isot. 109 (2015) 254-256.
