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The variety of radiopharmaceuticals used in nuclear medicine and amount of procedures are constantly growing. The activity of radiopharmaceuticals, which are administered for diagnostic and therapeutic purposes, strongly depends on the accuracy of the measuring equipment. According to international recommendations the dosimetry instrumentation should be traceable to a Secondary Standards Laboratory. The activity meters are not absolute assay systems, this equipment should be calibrated directly or indirectly, using standard reference sources traceable to absolute assay systems. The measurements of radionuclides with an activity meter are susceptible to geometrical influences and the container type, for radionuclides that emit beta-radiation or low-energy X-ray, gamma-photons. In this study the accuracy evaluation of activity meters was performed from 2016 to 2021.
The measurements of sixteen activity meter calibrators that are used in four Lithuanian hospitals that provide nuclear medicine procedures with diagnostics and therapeutic radiopharmaceuticals were compared with the readings of the secondary standard chamber Capintec CRC-15R (4π γ ionization chamber), No. 158488 brought to hospitals by the Ionizing Radiation Metrology Laboratory of the FTMC which is the National Metrology Institute (NMI) in Lithuania. The portable ionization chamber Capintec CRC-15R is used in parallel with a stationary ionization chamber Fidelis No. 06048, calibrated by National Physical Laboratory.
Data of 151 activity meter readings of activity of diagnostic, therapeutic and calibration radionuclides in different sources and geometries were analyzed. For calibration sources, the results of 78% activity meters were within the ± 5% tolerance level, while for the therapy sources 60% of the measuring equipment were within the acceptance level (± 5%), and for diagnostic sources about 90% of activity meters were within the ± 10% tolerance level.
