Huq M S, Yue N, Suntharalingam N, Curran W J
Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Med Phys. 1998 Sep;25(9):1685-91. doi: 10.1118/1.598349.
With the availability of commercial three-dimensional (3D)-treatment planning systems, more and more treatment plans call for the use of noncoplanar conformal beams for the treatment of brain tumors. However, techniques for the verification of many noncoplaner beams, such as vertex fields which involve any combination of gantry, collimator, and table angles, do not exist. The purpose of this work is to report on the results of an algorithm and a technique that have been developed for the verification of noncoplanar vertex fields used in the treatment of brain tumors. This technique is applicable to any geometric orientation of the beam, i.e., a beam orientation that consists of any combination of gantry, table, and collimator rotations. The method consists of superimposing a central plane image of a correctly magnified vertex field on a lateral or oblique field port film. To achieve this, the 3D coordinates of the projection of the isocenter onto the film for lateral (or oblique) as well as the vertex fields are determined and then appropriately matched. Coordinate transformation equations have been developed that enable this matching precisely. A film holder has been designed such that a film cassette can be secured rigidly along the side rails of the treatment table. The technique for taking a patient treatment setup verification film consists of two steps. In the first step, the gantry, table, and collimator angles for the lateral (or oblique) field are set and the usual double exposures are made; the first exposure corresponds to that of the treatment portal with the isocenter clearly identified and the second one a larger radiation field so that the peripheral anatomy is visible on the film. In the next step, the gantry, table, and collimator angles are positioned for the vertex field and the table is moved laterally and vertically and the film longitudinally to a position that will enable precise matching of the isocenter on the film. A third exposure is then taken with the vertex portal. What is seen on the film is a superposition of a central plane image of the vertex field onto the image of the lateral or oblique field. This technique has been used on 60 patients treated with noncoplanar fields for brain tumors. In all of these cases, the coincidence of the projection of the isocenter for the lateral (or oblique) and the vertex fields was found to be within 3 mm.
随着商用三维（3D）治疗计划系统的出现，越来越多的治疗计划要求使用非共面适形射束来治疗脑肿瘤。然而，对于许多非共面射束的验证技术并不存在，例如涉及机架、准直器和治疗床角度任意组合的顶点野。本研究的目的是报告一种已开发出的用于验证脑肿瘤治疗中使用的非共面顶点野的算法和技术的结果。该技术适用于射束的任何几何取向，即由机架、治疗床和准直器旋转的任意组合构成的射束取向。该方法包括将正确放大的顶点野的中心平面图像叠加在侧野或斜野的端口片上。为实现这一点，要确定等中心在侧野（或斜野）以及顶点野胶片上投影的三维坐标，然后进行适当匹配。已开发出坐标变换方程以实现精确匹配。设计了一种胶片夹，使得胶片暗盒能够沿治疗床的侧轨牢固固定。获取患者治疗摆位验证片的技术包括两个步骤。第一步，设置侧野（或斜野）的机架、治疗床和准直器角度，并进行常规的两次曝光；第一次曝光对应于清晰显示等中心的治疗射野，第二次曝光对应较大的辐射野，以便在胶片上可见周边解剖结构。下一步，定位顶点野的机架、治疗床和准直器角度，将治疗床横向和纵向移动，将胶片纵向移动到能使胶片上等中心精确匹配的位置。然后用顶点野进行第三次曝光。胶片上显示的是顶点野的中心平面图像叠加在侧野或斜野的图像上。该技术已应用于60例接受脑肿瘤非共面野治疗的患者。在所有这些病例中，发现侧野（或斜野）和顶点野等中心投影的重合度在3毫米以内。
