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目的:研究呼吸运动对安装于Varian23EX加速器的KV X线锥形束CT(cone beamCT,CBCT)成像结果的影响。方法:利用自行研制的运动体模系统,模体直径分别为1、2和3 cm,设定横轴方向运动幅度分别为0.5、1.0和1.5 cm,纵轴方向分别为0.5、1.0和2.0 cm,体模往返运动频率分别为12、20和25次/min,模拟呼吸运动并行CBCT扫描。结果:1)实际直径分别为10、20和30 mm的静止体模CBCT图像清晰,无变形,测量的直径分别为9.8±0.66〔95%CI(9.1~10.5)mm〕、19.9±0.75〔95%CI(19.1~20.7)mm〕和(29.7±0.69)mm〔95%CI(29.0~30.4)mm〕,横轴方向和纵轴方向的大小与体模实际大小相符合,误差均<1 mm。2)横轴和纵轴方向的呼吸运动对体模CBCT成像都有明显的影响。与静止体模CBCT图像相比,横轴和纵轴方向的体模运动都使CBCT图像清晰度下降、变形以及体积增大。在设定的运动幅度和运动频率范围内,3种大小的运动体模CBCT图像在横轴方向和纵轴方向的大小都与设定的体模实际运动范围(模体直径加运动幅度)相符合,差值均<3 mm。结论:呼吸运动对CBCT成像影响明显,成像结果反应规律性呼吸运动物体的实际运动范围。
PURPOSE: To study the effect of respiratory motion on KV X-ray cone beam CT (CBCT) imaging installed on a Varian 23EX accelerator. Methods: By using the self-developed motion phantom system, the diameter of the phantom was 1, 2 and 3 cm respectively. The amplitude of motion in the horizontal axis was set as 0.5, 1.0 and 1.5 cm, and the longitudinal axis was 0.5, 1.0 and 2.0 cm , The reciprocation frequency of phantom was 12, 20 and 25 times / min respectively, and simulated respiratory motion was performed in parallel with CBCT scan. Results: 1) The CBCT images of stationary phantoms with actual diameters of 10, 20 and 30 mm were clear and without deformation, with diameters of 9.8 ± 0.66 [95% CI (9.1-10.5) mm], 19.9 ± 0.75 % CI (19.1 ~ 20.7) mm] and (29.7 ± 0.69) mm [95% CI (29.0 ~ 30.4) mm] .The sizes of the transverse and longitudinal axes were in accordance with the actual size of the phantom . 2) The respiratory motion in horizontal axis and longitudinal axis have significant effects on phantom CBCT imaging. Compared with stationary phantom CBCT images, phantom motion along the horizontal axis and the longitudinal axis both reduce the sharpness of the CBCT image, reduce the deformation and increase the volume. Within the set range of motion and frequency of motion, the size of CBCT images of the three sizes of motion phantom in the horizontal axis and the vertical axis are both equal to the set actual range of phantom motion (phantom diameter plus motion amplitude) Meet, the difference is <3 mm. Conclusion: Breathing exercise has obvious effect on CBCT imaging. The imaging results reflect the range of actual exercise of breathing exercise objects.