放射性125I粒子植入布源剂量分布的平面模型优化研究

Optimization of the planar model for dose distribution of radioactive 125I seed plane implantation

目的利用计算机三维治疗计划系统与几何学原理,创建125I粒子平面植入条件下剂量分布特征与等剂量分布曲线,探讨正六边形平面植入模型的剂量分布价值。方法利用计算机治疗计划系统创建125I粒子等边三角形分布、正方形分布、正六边形分布时剂量特征,求出1 000、3 000、6 000、9 000、12 000、15 000和20 000 cGy剂量分布曲线。计算距离平面植入中心点距离0、0.5、1.0、1.5、2.0和2.5 cm处剂量分布;利用几何学原理绘制边长为1、2、3、4 cm延申相套正六边形图形,并在大于等于2cm的边上加点,将包括中心点在内的点相连接。结果利用三维粒子治疗计划系统可以模拟出平面植入条件下等剂量曲线分布。在等边三角形、正方形、正六边形条件下,粒子距离中心超出2.0 cm、2.5 cm时,中心剂量低于10 Gy,需要增加粒子,提高中心剂量;绘制的正六边形中任意相邻三点的连线都构成等边三角形,且边长为1 cm。结论通过对不同平面几何形状125I粒子种植分布的等剂量曲线与几何学原理分析,正六边形中心加一颗粒子的分布模型,最符合剂量学均匀分布规律,对临床125I粒子植入治疗肿瘤具有十分重要的指导意义。

Objective To establish dose distribution characteristics and isodose curves of 125I seed plane implantation using computer three-dimensional treatment planning system(3 D-TPS) and geometric principles, and to explore the value of dose distribution in hexagonal plane implantationmodel.Methods By computer treatment planning system, dose characteristics of 125I seeds with equilateral triangular, square and hexagonal distributions were created, dose distribution curves of 1 000, 3 000, 6 000, 9 000, 12 000, 15 000 and 20 000 cGy were attained, and dose distribution at 0, 0.5, 1.0, 1.5, 2.0 and 2.5 cm distances from the implantation center were calculated. The hexagonal figure with 1 cm, 2 cm, 3 cm and 4 cm edge lengths was drawn using geometric principles, and the points, including those added on the edges larger than or equal to 2 cm and the central point were connected.Results The three-dimensional particle therapy planning system could be used to simulate the isodose curve distribution under plane implantation. Under the conditions of equilateral triangle, square and hexagon, when the distance between the particle and the center is more than 2.0 cm and 2.5 cm, and the central dose is less than 10 Gy, it is necessary to increase the central dose of the particle. The connection lines of any three adjacent points in the drawn hexagon all constitute equilateral triangle, and the edge length is 1 cm.Conclusion The distribution model of hexagonal center plus a particle is most accordant with the dose uniform distribution through analyzing the isodose curve and geometric principle of 125I seed implantation distribution with different plane geometry. And this would have special meaning for clinical 125I seed implantation treatment of tumors.