Calibration of diagnostic equipment in nuclear medicine: methodology, accuracy and clinical significance

Abstract

Background. Accuracy and reproducibility of quantitative data from hybrid imaging methods (PET/CT and SPECT/CT) are of key importance for diagnosis, monitoring and treatment planning of cancer patients. Calibration failures or insufficient quality control may result in significant deviations from standard SUV values, which may change clinical decisions. Development and implementation of standardized quality control (QC) and calibration procedures ensures data reliability, optimization of radiation dose and comparability of results between medical centers, especially in multicenter studies and international projects. It is known that the calculated SUV values ​​are affected by many technical factors, and without proper scanner calibration, biases and variability may occur that are not obvious during routine visual assessment. Therefore, international initiatives (QIBA, UPICT, EANM, etc.) and standards require ensuring the quantitative accuracy of PET measurements in multicenter studies. The accuracy and correctness of the information obtained from PET/CT (as well as SPECT/CT) images directly depend on the technical condition of the tomograph and require timely regular monitoring. According to the IAEA recommendations, modern PET scanners require periodic calibrations, and the main goal of quality control programs is to ensure that the images reliably reflect the distribution of the radiopharmaceutical in the patient's body. Without such a QA/QC system, the risk of measurement errors and a decrease in the reliability of studies increases, which in oncology can lead to errors in assessing the dynamics of the disease. Purpose of the study. The report is aimed at substantiating the importance and describing the methods of calibration and quality control of PET/CT and SPECT/CT equipment in clinical practice. The goal is to demonstrate how maintaining calibration accuracy (especially the SUV parameter) and performing regular QC according to NEMA and IAEA standards improve the stability of equipment operation, reduce the likelihood of errors and ensure high clinical accuracy of study results. Materials and methods. The Nuclear Medicine Center of the BMC UDP RK has implemented a comprehensive QA/QC program for hybrid PET/CT and SPECT/CT scanners. Equipment calibration includes inter-device calibration "scanner - dosimetric radionuclide calibrator". For this purpose, a homogeneous water cylindrical phantom with a known activity of a radiopharmaceutical (for example, ^18F) is scanned quarterly. The activity of the sample is preliminarily accurately measured by a dose calibrator traced to a national standard, which allows setting the calibration coefficient of the tomograph for the correct calculation of SUV. The criterion is obtaining a SUV value of ≈ 1.0 on the scan in the phantom with an acceptable deviation of no more than 10%; in practice, with strict adherence to the methodology, a deviation of ~5% is achieved. Additionally, time synchronization between the dose calibrator and the scanner is checked (to exclude decay errors when recalculating activity). SPECT/CT quality control is carried out in a similar mode. The uniformity of the gamma camera detectors is checked daily using a flat source (e.g. 57Co) or a flooded background phantom. System alignment tests (rotation center correction) and resolution checks are performed weekly and after service work. A Jaszczak phantom is used - a hollow cylinder with a set of radial rods and spherical inserts filled with a 99mTc solution. This phantom allows for a comprehensive assessment of the resolution, contrast and homogeneity of the SPECT image on different collimators, as well as to ensure the correct operation of the reconstruction algorithms and alignment with CT. The indicators obtained on the phantoms are compared with the manufacturer's passport values ​​​​and standard requirements (NEMA NU1 for gamma cameras, IEC / NEMA NU2 for PET, IAEA and European Association of Nuclear Medicine recommendations). If deviations outside the tolerance are detected, recalibration or maintenance of the equipment is immediately performed. All QC results are recorded, which allows tracking the dynamics of device characteristics over time. Conclusion. Calibration and regular quality control of PET/CT and SPECT/CT equipment are mandatory conditions for accurate and reliable operation of the nuclear medicine department. For oncology, where even small changes in SUV or image errors can affect treatment tactics, maintaining strict QC protocols is the key to reproducibility of results and trust from clinicians. Conducting tests according to international standards (NEMA, IAEA, EANM) ensures the comparability of studies between different centers and devices. The implemented QC system allows early detection of deviations in the scanners and prevention of failures, without waiting for critical deterioration or equipment failure. As a result, the number of technical errors and repeated studies is reduced, the dose for patients is optimized, and most importantly, the reliability of diagnostic information and the effectiveness of therapy monitoring are increased. This approach improves the quality of oncological care, providing doctors with correct quantitative data and stable images for making clinical decisions.

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