圆的标准方程预防放射治疗机头与治疗床碰撞的应用

Application of the standard equation of a circle to prevention of collision between the gantry and the couch

背景与目的:在放射治疗中,由于肿瘤靶区位置不同,需要配合治疗床左右或者上下移动。在移床距离较大的情况下,治疗床或患者与治疗机机头可能会发生碰撞。该研究旨在通过探讨治疗机机头的运动轨迹以及床运动的范围,避免因操作不慎导致治疗机机头与治疗床发生碰撞,减少此类事故的发生。方法:选择直线加速器Varian Trilogy,在治疗床空载、准直器零位的情况下,模拟共面照射,测量等中心点到机头表面中心的距离以及床的宽度和床的厚度。由于直线加速器Varian Trilogy的治疗床横截面为倒置的梯形,治疗床上表面最外缘一点距离等中心点最远,在发生碰撞的情况下,最先与治疗机头发生碰撞,所以取该点作为参考点。选取40组移床数据,计算参考点的坐标。参考点的横坐标为1/2床宽与床的左右位移之和。参考点的纵坐标为降床的距离。计算参考点横坐标与纵坐标的平方和,与旋转半径的平方比较,预判治疗床与治疗机机头是否发生碰撞,并进行实际验证。结果:纵坐标与横坐标平方和大于半径的平方时,治疗床与治疗机机头发生碰撞,与预判吻合。纵坐标与横坐标平方和等于半径的平方时,治疗床与治疗机机头发生0距离接触,处于临界点,与预判吻合。当纵坐标与横坐标平方和小于半径的平方时,治疗床与治疗机机头不会发生碰撞,与预判吻合。结论:通过计算测量,发现这种计算方法是可行的,可以有效避免治疗床和治疗机的机头碰撞。

Background and purpose： The radiation should move at the same direction in accordance with the position of the couch during radiotherapy due to the different location of gross target volume. However, under the condition of the long distance movement of the couch, collisions between the gantry and the couch （or the patients） may happen. To avoid the collisions between the gantry and the couch, the motion area confliction between the gantry and the couch was analyzed. Methods： The distance from isocenter to the surface center of linear accelerator head, and the width and the thickness of treatment bed were measured when the treatment bed was empty, and gantry and collimator were at zero position. Forty sets of bed movement data were collected. The sum of squares of X-and Y-coordinates of reference point was calculated and compared with squares of rotation radius. Then, it was anticipated whether the linear accelerator head will collide with treatment bed. Finally, practical verification was made. Results： Whether linear accelerator head collides with treatment bed depends on the difference between the sum of squares of X-and Y-coordinates and the squares of rotation radius. No collisions will happen when the sum of squares of X-and Y-coordinates is less than that of the squares of rotation radius. Conclusion： It is feasible to avoid collisions of linear accelerator head with treatment bed by comparing the sum of squares of X-and Y-coordinates of reference point with squares of rotation radius.