Li T, Schreibmann E, Yang Y, Xing L
Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847, USA.
Phys Med Biol. 2006 Jan 21;51(2):253-67. doi: 10.1088/0031-9155/51/2/005. Epub 2005 Dec 21.
On-board imager (OBI) based cone-beam computed tomography (CBCT) has become available in radiotherapy clinics to accurately identify the target in the treatment position. However, due to the relatively slow gantry rotation (typically about 60 s for a full 360 degrees scan) in acquiring the CBCT projection data, the patient's respiratory motion causes serious problems such as blurring, doubling, streaking and distortion in the reconstructed images, which heavily degrade the image quality and the target localization. In this work, we present a motion compensation method for slow-rotating CBCT scans by incorporating into image reconstruction a patient-specific motion model, which is derived from previously obtained four-dimensional (4D) treatment planning CT images of the same patient via deformable registration. The registration of the 4D CT phases results in transformations representing a temporal sequence of three-dimensional (3D) deformation fields, or in other words, a 4D model of organ motion. The algorithm was developed heuristically in two-dimensional (2D) parallel-beam geometry and extended to 3D cone-beam geometry. By simulations with digital phantoms capable of translational motion and other complex motion, we demonstrated that the algorithm can reduce the motion artefacts locally, and restore the tumour size and shape, which may thereby improve the accuracy of target localization and patient positioning when CBCT is used as the treatment guidance.
基于机载成像仪（OBI）的锥形束计算机断层扫描（CBCT）已在放射治疗诊所中可用，以在治疗位置准确识别靶区。然而，由于在获取CBCT投影数据时龙门架旋转相对较慢（通常360度全扫描约需60秒），患者的呼吸运动在重建图像中会导致严重问题，如模糊、重影、条纹和变形，这会严重降低图像质量和靶区定位。在这项工作中，我们提出了一种针对慢速旋转CBCT扫描的运动补偿方法，通过将特定患者的运动模型纳入图像重建，该模型是通过对同一患者先前获得的四维（4D）治疗计划CT图像进行可变形配准得到的。4D CT各期的配准产生了表示三维（3D）变形场时间序列的变换，或者换句话说，是器官运动的4D模型。该算法在二维（2D）平行束几何结构中通过启发式方法开发，并扩展到三维锥形束几何结构。通过使用能够进行平移运动和其他复杂运动的数字体模进行模拟，我们证明了该算法可以局部减少运动伪影，并恢复肿瘤大小和形状，从而在将CBCT用作治疗引导时提高靶区定位和患者定位的准确性。
