Objective To explore the dosimetric effects of the same number and activity of radioactive 125I seeds in different plane arrangements. Methods Simulated 9 distribution modes using 9 125I seeds were designed by three- dimensional treatment planning system (3D- TPS), and the isodose curves of 60 Gy, 80Gy, 130 Gy, 145 Gy and 200 Gy were obtained. The areas enclosed by the isodose curves, the longer and shorter radius of these isodose curves and the medical cost per unit area were calculated with the professional image analysis software. Results Obvious differences in areas enclosed by the isodose curves, the longer and shorter radius of these isodose curves and the medical cost per unit area existed between each other among the nine different distribution modes of 9 125I seeds. The distribution modes that had the maximum areas enclosed by 60 Gy, 80 Gy, 130 Gy, 145 Gy and 200 Gy isodose curves were x1.5y1.5, x1y1.5, x1y1, x1y1 and x0.5y1, respectively, with the corresponding areas of 1 583.86 mm2, 1 146.03 mm2, 768.30 mm2, 621.85 mm2 and 480.97 mm2, respectively. Conclusion The peripheral dose and the therapeutic efficacy are significantly influenced by the arrangement of 125I seeds when the same number and activity of the seeds are used. The dose distributions are more homogeneous when the maximum areas enclosed by the isodose curves are obtained.%目的：探讨同数量、同活度125I 粒子单平面不同排列的剂量分布及其效应。方法利用计算机三维治疗计划系统（3D- TPS）模拟9颗2．59×107 Bq 125I 粒子的9种排列方式，得出60 Gy、80 Gy、130 Gy、145 Gy 和200 Gy 等剂量分布曲线并计算曲线包含的面积、长径、短径及单位面积的医疗费用。结果粒子排列方式不同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。60 Gy、80 Gy、130 Gy、145 Gy 和200 Gy 等剂量曲线内面积最大的粒子排列方式分别为：x1．5y1．5、x1y1．5、x1y1、x1y1、x0．5y1，相应的面积分别为：1583．86、1146．03、768．30、621．85和480．97 mm2。结论125I 粒子数量、活度相同时，不同的排列方式显著影响周边剂量及治疗效果。相同等剂量曲线内面积最大时的粒子排列方式剂量分布较均匀，靶区内无剂量学冷点，可能会有较好疗效。
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