一种自动确定放疗原始等中心的新方法

目的:提出一种通过勾画标记点结构自动确定放疗原始等中心的方法（以下简称新方法），通过与常规方法作比较分析测试新方法的应用价值。方法:选取40例接受放射治疗的腹部肿瘤患者的定位CT图像，其中标记点出现在1层、2层CT层面各20例。使用常规方法（通过Eclipse计划系统的十字定位工具手动确定原始等中心），然后使用新方法（通过自动勾画标记点结构并进行位置计算自动确定放疗原始等中心），分析两种方法确定的原始等中心之间坐标的差异。此外，还手动勾画了标记点结构。结果:与手动勾画标记点结构相比，自动勾画20例2层CT图像中标记点的Dice相似性指数（DSC）值为（0.79±0.06），40例左右方向（x轴）偏差绝对值、腹背方向（y轴）偏差绝对值的均值分别为0.04、0.05 cm。标记点出现在2层CT图像的20例中，头脚方向（z轴）偏差绝对值的平均值、标准差、最大值、最小值分别为0.22、0.03、0.26、0.16 cm。结论:本文提出的新方法可以快速、精确地计算出放疗原始等中心坐标，特别是当标记点出现在2层CT图像时，可以有效弥补常规方法的缺陷。

A new method for automatically determining the original isocenter in radiotherapy

Abstract: Objective To propose a method fo rautomatically determining the original isocenter in radiotherapy by delineating the structure of marked points (hereinafter referred to as the new method), and to test its application value by comparing it with the conventional method. Methods The CT images of 40 patients with abdominal tumors who received radiotherapy were selected, in which the marked points appeared in the first or second CT slices, 20 cases in each. The original isocenter was manually determined by conventional method through the cross positioning tool of Eclipse planning system, and then the new method was used to automatically determine the original isocenter by automatically delineating the structure of marked points and calculating the position.The difference of coordinates between the original isocenters determined by the two methods was analyzed. In addition, the structure of marked points was manually delineated. Results Compared with manually delineated structure of marked points, the Dice similarity index (DSC) value of marked points automatically delineated in the second CT slice in 20 cases was (0.79±0.06). The mean values of the absolute values of the deviations in 40 cases were 0.04 cm and 0.05 cm in the left-right direction (x-axis) and ventral-dorsal direction (y-axis), respectively. In the 20 cases with marked points appearing in the second CT slice, the mean, standard deviation, maximum and minimum values of the absolute values of z-axial (head-foot directional) deviations were 0.22, 0.03, 0.26 and 0.16 cm, respectively. Conclusion The proposed method can quickly and accurately calculate the original isocenter coordinates in radiotherapy. Especially when the marked points appear in the second CT slice, it can effectively make up for the defects of conventional methods.