van Herk M, Bruce A, Kroes A P, Shouman T, Touw A, Lebesque J V
Radiotherapy Department, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis), Amsterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 1995 Dec 1;33(5):1311-20. doi: 10.1016/0360-3016(95)00116-6.
Knowledge about the mobility of organs relative to the bony anatomy is of great importance when preparing and verifying conformal radiotherapy. The conventional technique for measuring the motion of an organ is to locate landmarks on the organ and the bony anatomy and to compare the distance between these landmarks on subsequent computerized tomography (CT) scans. The first purpose of this study is to investigate the use of a three dimensional (3D) image registration method based on chamfer matching for measurement of the location and orientation of the whole organ relative to the bony anatomy. The second purpose is to quantify organ motion during conformal therapy of the prostate.
Four CT scans were made during the course of conformal treatment of 11 patients with prostate cancer. With the use of a 3D treatment planning system, the prostate and seminal vesicles were contoured interactively. In addition, bladder and rectum were contoured and the volume computed. Next, the bony anatomy of subsequent scans was segmented and matched automatically on the first scan. The femora and the pelvic bone were matched separately to quantify motion of the legs. Prostate (and seminal vesicle) contours from the subsequent scans were matched on the corresponding contours of the first scan, resulting in the 3D rotations and translations that describe the motion of the prostate and seminal vesicles relative to the pelvic bone.
Bone matching of two scans with about 50 slices of 256 x 256 pixels takes about 2 min on a workstation and achieves subpixel registration accuracy. Matching of the organ contours takes about 30 s. The accuracy in determining the relative movement of the prostate is 0.5 to 0.9 mm for translations (depending on the axis) and 1 degree for rotations (standard deviations). Because all organ contours are used for matching, small differences in delineation of the prostate, missing slices, or differences in slice distance have only a limited influence on the accuracy. Rotations of the femora and the pelvic bone are quantified with about 0.4 degree accuracy. A strong correlation was found between rectal volume and anterior-posterior translation and rotation around the left-right axis of the prostate. Consequently, these parameters had the largest standard deviations of 2.7 mm and 4.0 degrees. Bladder filling had much less influence. Less significant correlations were found between various leg rotations and pelvic and prostate motion. Standard deviations of the rotation angles of the pelvic bone were less than 1 degree in all directions.
Using 3D image registration, the motion of organs relative to bony anatomy has been quantified accurately. Uncertainties in contouring and visual interpretation of the scans have a much smaller influence on the measurement of organ displacement with our new method than with conventional methods. We have quantified correlations between rectal filling, leg motions, and prostate motion.
在准备和验证适形放疗时，了解器官相对于骨骼解剖结构的移动性非常重要。测量器官运动的传统技术是在器官和骨骼解剖结构上确定标志点，并在后续的计算机断层扫描（CT）上比较这些标志点之间的距离。本研究的首要目的是研究基于倒角匹配的三维（3D）图像配准方法在测量整个器官相对于骨骼解剖结构的位置和方向中的应用。第二个目的是量化前列腺适形治疗期间的器官运动。
在对11例前列腺癌患者进行适形治疗的过程中进行了4次CT扫描。使用3D治疗计划系统，交互式勾勒出前列腺和精囊的轮廓。此外，勾勒出膀胱和直肠的轮廓并计算其体积。接下来，对后续扫描的骨骼解剖结构进行分割，并自动与第一次扫描进行匹配。分别对股骨和骨盆进行匹配以量化腿部的运动。将后续扫描的前列腺（和精囊）轮廓与第一次扫描的相应轮廓进行匹配，从而得出描述前列腺和精囊相对于骨盆运动的3D旋转和平移。
在工作站上，对约50层256×256像素的两次扫描进行骨骼匹配大约需要2分钟，并实现亚像素配准精度。器官轮廓的匹配大约需要30秒。确定前列腺相对运动的平移精度（取决于轴）为0.5至0.9毫米，旋转精度为1度（标准差）。由于所有器官轮廓都用于匹配，前列腺轮廓描绘的微小差异、缺失切片或切片距离差异对精度的影响有限。股骨和骨盆的旋转量化精度约为0.4度。发现直肠体积与前列腺前后平移以及绕左右轴的旋转之间存在强相关性。因此，这些参数的标准差最大，分别为2.7毫米和4.0度。膀胱充盈的影响要小得多。在各种腿部旋转与骨盆和前列腺运动之间发现的相关性较弱。骨盆骨旋转角度的标准差在各个方向上均小于1度。
使用3D图像配准，已准确量化了器官相对于骨骼解剖结构的运动。与传统方法相比，扫描轮廓绘制和视觉解读中的不确定性对我们新方法测量器官位移的影响要小得多。我们已经量化了直肠充盈、腿部运动和前列腺运动之间的相关性。
