Based on the calibration method in the IAEA TRS 457 report, RQT 8 radiation quality was established. The spectra and angular distributions for RQT 8 radiation quality was performed by Monte Carlo simulation software EGSnrc with the distance of 95 cm, radius of 5 cm between tube focal spot and recording planar, which constructing the model of CT chambers calibration field. The effection of calibration CT chambers was studied under additional aperture with different length as well as angle edges. The result shows that the deviation of established...