中文摘要：

目的定制125I放射性粒子植入计划的优选方案。方法将125I粒子等间距植入直径为1、2和3cm的3种球形模体和三径分别为1cm×1cm×2cm、1cm×1cm×3cm、1cm×2cm×2cm、1ccm×2cm×3cm、1cm×3cm×3cm、2cm×2cm×3cm和2cm×3cm×3cm的7种椭球形模体，粒子分布均匀对称，调整粒子活度和间距，使靶区剂量满足处方剂量D90145Gy，并实现尽可能适形均匀的剂量分布。初始粒子间距是1cm，为改善靶区剂量分布适形度和均匀性，将粒子间距调整为0．75cm。通过评价均匀性指数（HI）、靶区外体积指数（EI）和适形指数（cI）定制粒子植入优选方案。同时记录植入粒子活度和数目。结果对直径1cm的球形靶区，粒子间距1和0．75cm时H1分别为40．0％和55．9％，E1分别为98．3％和95．1％，CI均为0．44；对直径3cm的球形靶区和1cm×2cm×2cm的椭球形靶区，粒子间距1cm植入方式的HI、EI和CI优于粒子间距0．75cm的植入方式。对其余靶区粒子间距0．75cm植入方式的E1和cI均优于间距1cm的植入方式，HI略小于间距1cm的植入方式。粒子间距0．75和1cm植入单颗粒子活度分别为17．0～27．8MBq和30．0～58．8MBq，间距0．75cm比间距1cm多植入粒子2—10颗。结论对于10种靶区，除直径为1cm、3cm的球形靶区和1cm×2cm×2cm的椭球形靶区以外，其余7种靶区0．75cm植入方式的剂量分布适形度更好，靶区外接受处方剂量体积更小，为粒子均匀植入的优选方案。

英文摘要：

Objective To customize the optimal plans for radioactive 125I seeds volumetric implants in selected regular target volumes. Methods 125I seeds were symmetrically and uniformly implanted into 3 spherical targets with the diameters of 1, 2 and 3 cm and 7 ellipsoidal targets with the 3 dimensions ofl cm×1 cm×2 cm, 1 cm×1 cm×3 cm, 1 cm×2 cm×2cm, 1 cm×2 cm×3 cm, 1 cm ×3 cm×3 cm, 2 cm×2 cm×3 cmand 2 cm×3 cm×3 cm. The activity and inter-space of seeds were adjusted to obtain the conformal and uniform dose distribution, with the prescribed D90 （the dose delivered to 90% of the targets） greater than 145 Gy. The inter-space of seeds was changed from 1 cm to 0. 75 cm, to improve the conformity and uniformity of dose distribution. Plan quality was assessed using homogeneity index （ HI）, external index （EI） and conformal index （CI）. The activity and number of seeds implanted were also recorded and compared. Results For the spherical target with the diameter of 1 cm, when seeds were implanted with the inter-space of 1 cm and 0. 75 cm, the HI were 40. 0% and 55.9% , the EI were 98.3% and 95.1% , the CI were 0.44 and 0.44, respectively. For the spherical target with the diameter of 3 cm and the target with the 3 dimensions of 1 cm × 2 cm × 2 cm, the implant with the inter-space of 1 cm provided better indices of HI, EI and CI than those with the inter-space of 0. 75 cm. For the other targets, the implants with the inter-space of 0.75 cm provided better indices of EI and CI than those with the inter-space of 1 cm, although they displayed a little worse homogeneity in terms of HI. The activity per seed was 17.0 - 27.8 MBq and 30. 0 - 58.8 MBq in the implants with the inter-spaces of 0.75 cm and 1 cm, respectively. 2 - 10 more seeds were needed in the implants with the inter-space of 0. 75 cm. Conclusions For the studied targets except the spherical targets with the diameter of 1 cm and 3 cm and the ellipsoidal target with the dimension of 1 cm × 2 cm × 2 cm, 125I seeds implanted with the inter-spa