Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
Phys Med Biol. 2009 Dec 7;54(23):7135-50. doi: 10.1088/0031-9155/54/23/007. Epub 2009 Nov 11.
External beam radiation treatment for patients with cervical cancer is hindered by the relatively large motion of the target volume. A hybrid MRI-accelerator system makes it possible to acquire online MR images during treatment in order to correct for motion and deformation. To fully benefit from such a system, online delineation of the target volumes is necessary. The aim of this study is to investigate the accuracy of rigid, non-rigid and semi-automatic registrations of MR images for interfractional contour propagation in patients with cervical cancer. Registration using mutual information was performed on both bony anatomy and soft tissue. A B-spline transform was used for the non-rigid method. Semi-automatic registration was implemented with a point set registration algorithm on a small set of manual landmarks. Online registration was simulated by application of each method to four weekly MRI scans for each of 33 cervical cancer patients. Evaluation was performed by distance analysis with respect to manual delineations. The results show that soft-tissue registration significantly (P < 0.001) improves the accuracy of contour propagation compared to registration based on bony anatomy. A combination of user-assisted and non-rigid registration provides the best results with a median error of 3.2 mm (1.4-9.9 mm) compared to 5.9 mm (1.7-19.7 mm) with bone registration (P < 0.001) and 3.4 mm (1.3-19.1 mm) with non-rigid registration (P = 0.01). In a clinical setting, the benefit may be further increased when outliers can be removed by visual inspection of the online images. We conclude that for external beam radiation treatment of cervical cancer, online MRI imaging will allow target localization based on soft tissue visualization, which provides a significantly higher accuracy than localization based on bony anatomy. The use of limited user input to guide the registration increases overall accuracy. Additional non-rigid registration further reduces the propagation error and negates errors caused by small observer variations.
宫颈癌患者的外部射束放射治疗受到靶区较大运动的阻碍。混合 MRI-加速器系统使得在治疗期间获取在线磁共振图像成为可能，以便对运动和变形进行校正。为了充分利用这种系统，有必要对靶区进行在线勾画。本研究旨在探讨刚性、非刚性和半自动配准在宫颈癌患者分次间轮廓传播中的准确性。基于骨性解剖结构和软组织对互信息进行了配准。使用 B 样条变换进行非刚性方法。半自动注册使用点集注册算法在手动标记的小数据集上实现。对 33 例宫颈癌患者的每周 4 次 MRI 扫描分别应用每种方法进行在线注册模拟。通过与手动勾画的距离分析来评估。结果表明，与基于骨性解剖结构的配准相比，软组织配准显著（P < 0.001）提高了轮廓传播的准确性。用户辅助和非刚性配准的组合提供了最佳结果，中位误差为 3.2 毫米（1.4-9.9 毫米），而骨性配准为 5.9 毫米（1.7-19.7 毫米）（P < 0.001），非刚性配准为 3.4 毫米（1.3-19.1 毫米）（P = 0.01）。在临床环境中，通过对在线图像进行目视检查去除异常值，可以进一步提高益处。我们得出结论，对于宫颈癌的外部射束放射治疗，在线 MRI 成像将允许基于软组织可视化的靶区定位，这比基于骨性解剖结构的定位提供了更高的准确性。使用有限的用户输入来指导注册可以提高整体准确性。额外的非刚性配准进一步降低了传播误差，并消除了由于观察者微小变化引起的误差。
