摘要
目的:研究放射治疗病人的不同呼吸运动状态对CT模拟定位扫描的图像重建精度的影响以及对放射治疗计划设计和评估的影响。方法:使用动态体模模拟放疗患者肺部靶区的呼吸运动,测试和计算不同运动周期和幅度下用于治疗计划设计的CT扫描的图像重建几何体积的变化。体模运动单元包含1cm和2cm的两个统一密度的球体和边长3cm的正方体,分别设定在沿CT定位床轴向以±1cm和±2cm的幅度作运动周期为3s,4s,5s,6s和10s的匀速振动。CT扫描条件为螺距1.5,层厚5mm,扫描速度1Slice/s。在CT模拟定位工作站上对扫描的原始数据进行三维图像重建,以自动阈值勾画方式计算模拟靶区体积大小,并与体模的实际几何体积比较确定误差。结果:(1)在体模运动方向有明显的几何体积误差,且可能形成明显的成像间隙。(2)重建的模拟运动靶区体积变化与其物理体积大小和运动状态相关。在选定的CT扫描参数和靶区体积的运动状态下,CT扫描图像重建的体积误差最大达66.7%,在振幅为2cm时相隔2cm的模体图像甚至可能发生部分重迭。(3)靶区图像的几何中心可能发生偏差,从而造成治疗计划设计的射野中心偏差。结论:在呼吸运动幅度和周期分别大于2cm和4s时有必要对定位患者采取呼吸限制方式进行CT模拟定位扫描或根据实际测量结果评估靶区体积误差可能带来的计划误差。
Objective： A QUASAR respiration motion phantom was used to study the aliasing of target volume encountered when acquiring treatment planning CT＇s of a moving target in lung. Materials and Methods： The unit was programmed for （S/I） displacements of± 1 cm and ± 2 cm respectively, about apoint,with initial phase 0 or 7r with period of 3 s, 4 s, 5 s, 6 s, 10 s. Targets consisted of two spheres of unit density, 1 cm and 2 cm in diameters and a cube,3 cm in side length. Spiral CT scanning was performed on CT scanner （Siemens） on both stationary and dynamic targets. A pitch of 1.5 was used to acquire CT scan slices of thicknesses 5 mm. Scanspeeds of 1 s were investigated, and a consistent image acquisition to motion phase synchronization scheme was used on all scans that involved moving targets. Result： （1） While moving, there are obviously volume aliasing on S/I direction. Geometric miss, which is predominantly observed at the S/I extremes of the moving target image; （2）The size of target and the motion state both effect Volume aliasing. The max difference of volume reach to 66.7%. While amplitude is 2 cm, target volumes between 2 cm will partly overlapped; （3） Geometric centre of the target volume also changed. Conclusion： When speacial setup, we ought to limit the motion of the patient if his organ amplitude reach to 2 cm and his respiratory cycle is above and beyond 4 s.With the real amplitude of the motion state which directly effect the speacial integrity of target volume. Or evaluating the discrepancy of the plan which based on aliasing of target volume with measured result.
出处
《中国医学物理学杂志》
CSCD
2007年第6期391-395,414,共6页
Chinese Journal of Medical Physics
关键词
放射治疗
CT模拟定位
呼吸运动
图像重建
radiotherapy
spiral CT
respiration motion phantom
image reconstruction
