利用计划系统对不同参数携带^125I粒子食管支架剂量学分析

Brachytherapy treatment planning calculation ^125I particle esophageal stent dosimetric study

目的研究不同粒子间距、不同直径和不同长度^125I粒子支架在不同^125I粒子活度下的剂量学分布特性，推导^125I粒子食管支架的剂量表，为其临床应用提供剂量学的依据。方法设计不同长度、不同直径、不同粒子间隔的携带放射性^125I粒子的自膨式覆膜食管支架，将装有假源的食管支架垂直固定于装有固体石蜡（分析纯）熔液的圆柱形有机玻璃模型（厚度0．8（3111，直径20cm，高度20cm）内，待石蜡冷却凝固后，采用CT扫描，将图像信息传人治疗计划系统（TPS）。以支架的中心点为圆点，在0。和90。分别模拟距离圆点1．5、2．0、2．5、3．0、3．5、4．0、5．0、6．0和8．0cm处的累积剂量。结果粒子间距为1．0和1．5em的径向累积剂量在18．5、22．2、25．9、29．6、33．3、37．0MBq分别相差4．8％、5．8％、7．2％、8．0％、8．6％和13．3％；当粒子间距和支架长度相同时，支架直径1．3、2．0和2．4cm时的径向累积剂量在各点时分别相差4．9％比3．4％、4．7％比3．8％、5．4％比6．6％、4．5％比5．3％、4．7％比4．8％、4．8％比5．4％；当粒子间距和支架直径相同时，支架长度8、12和16cm时的径向累积剂量在各点时分别相差1．9％比1．2％、1．7％比0．8％、1．6％比1．3％、1．9％比1．5％、1．7％比1．8％、1．6％比1．3％。结论^125I粒子支架的径向累计剂量与放射性粒子的活度呈正相关，即^125I粒子支架某一点的剂量率随放射性粒子活度的增加而增加。

Objective To investigate the dosimetric distribution characteristics of ^125I seed steuts with different seed spacing, diameter and length, as well as different ^125I seed activity. The dosimetry table of ^125I seed esophageal stent was derived to provide dosimetry for its clinical application. Methods The self-expanding coated esophagus stent was designed to carry radioactive ^125I seeds with different length, diameter and seed spacing. A cylindrical organic glass model （ Thickness 0. 8 cm, diameter 20 cm, height 20 cm） was fixed vertically to a cylindrical organic glass containing a solid paraffin （analytical pure ） solution. After paraffin cooling and solidification, CT scan was used to transmit image information to TPS. With the center of the bracket as a dot, the cumulative dose at a distance of 1.5,2.0,2. 5,3.0,3.5,4. 0, 5.0,6. 0 and 8.0 cm away from the dot was simulated respectively in 0° and 9° direction. Results The radial cumulative dose with the seed spacing which was 1.0 and 1.5 cm were different by 4. 8% , 5.8% , 7.2%, 8.0%, 8.6% and 13.3% respectively under the exposure of 18.5,22. 2,25.9,29. 6,33.3 and 37.0 MBq. When the seed spacing was the same as the length of the stent, the radial cumulative dose with the stent which diameter was 1.3, 2. 0,2. 4 cm were different by 4. 9% vs 3.4% ,4. 7% vs 3.8% ,5.4% vs 6. 6% ,4. 5% vs 5.3% ,4. 7% vs 4. 8% ,4. 8% vs 5.4% respectively under the exposure of 18.5,22. 2, 25.9,29.6,33.3 and 37.0 MBq. When the seed spacing was the same as the diameter of the stent, the radial cumulative dose with the stent which length was 8,12,16 cm were different by 1.9% vs 1.2% , 1.7% vs0.8%, 1.6% vs 1.3%, 1.9% vs 1.5%, 1.7% vs 1.8%, 1.6% vs 1.3% respectively under the exposure of 18.5,22. 2,25.9,29. 6,33.3 and 37.0 MBq. Conclusions The radial cumulative dose of the ^1251 seed stent is positively correlated with the activity of the radioactive seeds, Which means the dose rate of a certain point of the ^125I seed stent increase with the increase of the activity of the radioactive seeds. The stent of the ^125I radioactive seeds is negatively correlated with the distance, the dose rate of the ^125I seed stents decrease rapidly with the increase of distance.