To present a more effective way to determinate the target volume in electron beam irradiation while using three - dimensional treatment planning system. [ Methods] Contoured the target volume according to the images from CT simulation, and designed the electron beam irradiation field by using 3DTPS. Calculated the shifting coordinate of irradiation field based on the original coordinate. Installed the applicator with the leaden block of electron beam onto the accelerator. Turned on the lamp field and marked the cross line on the plate. A foam mould which was marked with filed centre and direction should be cutted based on the DR image from TPS. The leaden block would be made on a premise that the cross lines on the plate and the foam were coincident. Evaluated the feasibility of this method by radiotherapy verification. [Results] The offset degree of target centre was less than 2. 2 mm, also the maximum deviation is less than 1. 7 mm. [ Conclusion] The method that coincide the irradiation field centre and the centre from TPS can solve the problem of target areas variation. Also the method can ensure the process of electron irradiation going smoothly.%[目的]探讨三维治疗计划系统设计的电子束照射野在放射治疗过程中靶区位置准确确定的方法.[方法]采用CT模拟定位,在CT图像上勾画靶区,使用三维治疗计划系统进行电子束照射野计划设计,并根据定位参考坐标计算出靶区中心的移动摆位坐标；在加速器托架上插入合适规格的电子束限光筒,末端放入与其相匹配的电子束挡块模具(内嵌配套规格影子板),打开灯光野,将加速器中心十字线标记在影子板上；根据计划系统打印带中心十字线的照射野DRR图切割出照射野泡沫阳模,并在泡沫阳模上标记射野中心十字线和方向；将泡沫模块上的十字线与模具中影子板上十字中心线相重合,制作电子束挡块；加速器上按靶区的摆位坐标移床找到靶区中心,插上限光筒,放入电子束挡块,验证该方法的可行性.[结果]靶区中心点位置最大偏差≤2.2 mm,照射野边缘最大偏差≤1.7 mm.[结论]利用电子束射野挡块铅窗中心与加速器治疗中心相一致的方法,很好的解决了三维治疗计划系统设计电子束野治疗摆位靶区位置难以确定问题,能够提高电子束适形治疗的准确性.
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