KV X线锥形束CT呼吸运动目标成像的体模研究

Effect of respiratory motion on KV X-ray cone beam CT image

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。

OBJECTIVE： To evaluate the effect of respiratory motion on imaging results of KV X-ray cone beam CT （CBCT） equipped on Varian 23EX linear accelerators. METHODS： A phantom system consisted of a mobile flatform and three solid acrylic balls （1, 2 and 3 cm in diameter, respectively） was devised to simulate respiratory motion, while the conebeam CT images were acquired. The peak-to-peak amplitude was0.5, 1.0, 1.5 cm in X axis, and0.5, 1.0 and 2.0 eminZ axis with a frequency of 12, 20, 25 per minute, respectively. RESULTS： The images of static phantom were limpid and undeformed, and its magnitudes were in accordance with real size, with measured diameters 9.8±0.66[95%CI（9.1-10.5） mm], 19.9±0.75[95%CI （19.1--20.7） mm], 29.7±0.69 [95%CI （29.0--30.4） mm] mm vs. the real size 10, 20 and 30 mm, respectively, with error 〈 1 mm. The simulated respiratory motion had significant effects on CBCT images of the phantom in both transverse axis and long axis. Significant decrease in image legibility and increase in deform and volume were observed when the motion amplitude was increased. No significant effects on image results related to respiratory frequency change was observed. In this study, all CBCT images showed accordance with the range of phantom movement （the magnitude of the phantom plus the motion amplitude）, with difference 〈3 mm. CONCLUSION： This phantom study indicates that CBCT image includes the data of respiratory motion.