Accuracy and Linearity Tests of Dose Calibrators in Nuclear Medicine Centers in Iran: The Role of Secondary Standard Dosimetry Laboratory in Quality Control and Maintaining Activity Traceability in Compliance with International Standards

Abstract

Advancements in nuclear medicine have provided remarkable opportunities for the diagnosis and treatment of diseases. One of the key components of these advancements is radiopharmaceuticals, which play a crucial role in disease detection and patient treatment management. However, the accuracy of measuring the injected activity is essential for their effectiveness. To ensure precise activity estimation before administration to a patient, radionuclide calibrators are used. Therefore, it is crucial that this equipment meets its performance requirements. According to sub-clause 3.167 of the GSR Part 3 document issued by the International Atomic Energy Agency (IAEA), the traceability of dosimetry equipment calibration to a standard dosimetry laboratory is mandatory. In Iran, this responsibility lies with the Secondary Standard Dosimetry Laboratory (SSDL), which is in charge of monitoring and maintaining the traceability of radionuclide activity. The laboratory, as the only accredited facility in this field, conducts annual calibrations of dose calibrators used in nuclear medicine centers across the country. Currently, there are more than 245 nuclear medicine centers in the country. The aim of this study is to evaluate and compare the performance of dose calibrators used in 130 Nuclear Medicine Centers through standard tests, including measurement accuracy for eight radionuclides (Cs-137, Ba-133, Co-57, Tc-99m, I-131, Lu-177, F-18, and Ga-68) and linearity (using the Tc-99m source). The study examines dose calibrators from AEOI (Iran), AMERSHAM Inc. (USA), BIODEX (USA), CAPINTEC Inc. (USA), COMECER (Netherlands), ISOMED (Germany), PICKER (USA), PTW (Germany), and SIEMENS (Germany) across these centers. The acceptable accuracy limits for the Dose Calibrator Reference Standard compared to the secondary standard are ±2%, and for field devices, they are ±5%. If the error percentage is less than 5%, the device does not require a calibration factor adjustment (±5%), indicating its accuracy and reliability. However, if the error exceeds 10%, it suggests instability or excessive gas leakage over the year, requiring service. For errors between 5% and 10%, a new calibration factor is determined to minimize the discrepancy. For optimal performance, accuracy and linearity should be within ±5%. The responses of 150 dose calibrators used in Nuclear Medicine Centers were compared with the Dose Calibrator Reference Standard to assess their accuracy. All dose calibrators were evaluated according to the Measurement Good Practice Guide No. 93 standard. The percentage of dose calibrators within the acceptable ±5% error range was 82.2% for Cs-137, 81.8% for Ba-133, 85.33% for Co-57, 89% for Tc-99m, 82.9% for I-131, 78.5% for Lu-177, 66.6% for Ga-68, and 75% for F-18. The radionuclide calibrators’ linearity was within ±5%, except for 5 cases that showed deviations and required servicing. An appropriate quality control program is essential for ensuring the accuracy of the administered patient dose. In Iran, the Secondary Standard Dosimetry Laboratory ensures the integrity of the metrological traceability chain for radioactivity measurement.