125I粒子平面布源剂量学研究

Study on dosimetry of 125I seed in-plane implantation

目的 探讨同活度、同数量125I粒子单平面不同排列的剂量学效应.方法 利用计算机三维治疗计划系统（3D-TPS）模拟9颗2.035×107Bq125I粒子的9种分布模式：按粒子排列间距（以x轴、y轴方向计,单位为cm）分x0.5、y0.5,x0.5、y1.0,x0.5、y1.5,x1.0、y1.0,x1.0、y1.5,x1.5、y1.5,x0.5、y0.5（2）1.0（即第1,3列粒子y向间距0.5 cm,第2列粒子间距y向1.0 cm）,x0.5、y1.0（2）0.5（即第1,3列粒子y向间距1.0cm,第2列粒子y向间距0.5 cm）,x1.0、y1.0（2）0.5（即第1,3列粒子y向间距1.0 cm,第2列粒子y向间距0.5 cm）.用专业图像分析软件计算出40,80,130,145和200 Gy剂量分布曲线及曲线包含的面积、长径、短径,再用公式计算：单位面积的医疗费用=（单颗粒子价格＋单颗粒子手术费）×粒子数/等剂量曲线包含面积.结果 粒子不同分布时相同等剂量曲线包含的面积、长径、短径和单位面积的医疗费用存在差异.40,80,130,145和200 Gy等剂量曲线内面积最大的粒子排列分别为：x1.5、y1.5,x1.0、y1.0,x1.0、y1.0,x0.5、y1.0,x0.5、y1.0,对应的面积分别为：1672.31,849.08,524.50,481.20和350.92 mm2.结论 同活度、同数量125I粒子的不同分布模式直接影响周边剂量.

Objective To study the dosimetry of different arrangements of 125I seeds in one plane.Methods Nine different in-plane arrangements of 9 125I seeds （2.035 × 107 Bq/seed） were simulated according to distance （cm） along x （horizontal）- and y（ longitudinal ）-axis using the 3-dimensional treatment planning system （TPS） （3D-TPS）： x0.5, y0. 5 x0. 5, y1.0 x0. 5, y1.5 x1.0, y1.0 x1.0, y1.5 x1.5, y1.5 x0. 5, y0. 5 （2）1.0 x0.5, y1.0 （2）0.5 x1.0, y1.0 （2）0.5. The isodose curves of 40,80, 130, 145 and 200 Gy were created and the area, radius and medical cost under the 40, 80, 130, 145and 200 Gy isodose curves were calculated. Results The area, radius and medical cost under the same isodose curves were significantly different with each 125I seed arrangement. The arrangements which had the biggest area under curves of 40, 80, 130, 145 and 200 Gy isodose were x1. 5, y1. 5 x1. 0, y1. 0 x1. 0,y1. 0 x0. 5, y1. 0 and x0. 5, y1. 0, respectively. Conclusion The matched peripheral dose and therapeutic effect were affected significantly by the geometric arrangement of 125I seeds.