Establishment of diagnostic X-ray air kerma standard in Taiwan

Abstract

Diagnostic X-ray air kerma standards were established at the Institute of Nuclear Energy Research (INER, Taiwan) in accordance with the recommendations of IEC 61267. The radiation qualities established by INER include IEC 61267 RQR (RQR 3-10), RQA (RQA 3-10) and RQT. Among them, RQR is used to simulate the energy spectrum generated from the X-ray machine, RQA is used to simulate the energy spectrum after passing through the human body, and RQT is used to simulate the energy spectrum in computed tomography (CT).A tungsten target X-ray machine, 99.9% pure aluminum and copper filters were used to build the IEC 61267 radiation qualities. A cylindrical free-air chamber (FAC) is used as the X-ray air kerma primary standard. The FAC correction factors, including air attenuation, window attenuation, ion recombination, photon-scattering, electron-loss and shadow-effect, were evaluated by experiments or Monte Carlo methods.The half value layers (HVL) of these radiation qualities were measured by FAC, and the HVL differences between INER and IEC 61267 are less than 3%. The uncertainty of measurement was evaluated according to ISO GUM, and the relative standard uncertainty of primary standard is 0.53% (k = 1). An ionization chamber (Exradin A5) was sent to PTB and calibrated with IEC 61267 RQR and RQA qualities. When comparing the calibration factors between PTB and INER, the differences are less than 1.25%.The air kerma standard of diagnostic X-ray has been established at INER, and it will provide dose calibration services in Taiwan to improve medical quality.