锥形束CT联合六自由度床的校位精度分析

The positioning accuracy study of the cone-beam computed tomography in combination with the sixdegree couch table

目的 检测并分析我院引进的医科达图像引导放疗系统的锥形束CT（CBCT）的机械稳定性,及其联合六自由度床（HRTT）在放疗摆位时的校位精度.方法 测量X射线容积图像（XVI）系统的机械稳定性和重复性;研究可动部件（千伏级射线探测板和源方向球管支臂）的伸缩对XVI图像匹配结果的影响;同时比较骨配准和灰度值配准的精度;测量并分析HRTT在线性方向（x、y、z）和旋转方向（u、v、w）的校位精度.结果 XVI系统自身在线性和旋转方向上的重复性偏差分别≤0.4 mm和≤0.3°,说明该系统有较好的机械稳定性.HRTT联合XVI系统的总平均校位精度在线性方向和旋转方向分别≤0.6mm和≤0.4°.同时研究发现灰度值配准在精度上高于骨配准.结论 XVI系统的图像采集和配准过程具有较高的机械稳定性和较好的重复性;HRTT校正线性和旋转方向的摆位误差具有较高精度,其空间六自由度的校位功能结合CBCT技术的图像功能实现了图像引导放疗技术的临床应用.

Objective To scrutinize the positioning accuracy and reproducibility of the cone-beam computed tomography system in combination with the six-degree couch table （Hexapod Robot Treatment Table, HRTT）. Methods The mechanical stability of the X-ray volume imaging （XVI） system was tested,in terms of the reproducibility. And the influence of the moveable parts, including the KV panel and the source arm, on the accuracy of the XVI image registration was analyzed. The accuracy between the bone and grey value registration was compared using a head-and-neck phantom. The accuracy of the HRTT for translational, rotational, and a combination of translational and rotational corrections was investigated in consecutive measurements. Results The performance of XVI system itself was stable with translational and rotational error of below 0. 4 mm and below 0. 3°, respectively. The mean position accuracy of the XVI system in combination with the HRTT summarized over all measurements was below 0. 6 mm and below 0. 4° for translational and rotational corrections, respectively. The grey value match was more accurate than the bone match. Conclusions The XVI image acquisition and registration procedure were highly reproducible.Both translational and rotational positioning errors can be corrected very precisely with the HRTT. The HRTT is therefore well suited to complement CBCT to take full advantage of position correction in six degrees of freedom for image guided radiotherapy.