立体定向放射治疗中靶外剂量分布的研究

Study on the distribution of doses outside target in stereotactic radiation treatment

目的掌握SGS-1型立体定向放射治疗（SRT）系统的基本防护性能指标、靶外剂量分布及其影响因素，以便更好地设计治疗计划系统（TPS）和实施方案，保护靶外正常组织并提高疗效。方法以SGS-1型SRT系统为研究对象，使用焦点测量棒、胶片（MD-55和Kodak）、有机玻璃球形模体、PTWUNIDOS放疗剂量仪、LiF（Mg、Cu、P）热释光剂量计（TLD）等检测工具，并借助Duoscan扫描软件与DFS剂量胶片分析处理系统等对该SRT系统的基本防护性能和靶外荆量分布进行测量和分析。结果机械定位基准中心与聚焦靶区中心的偏差为0．28mm，靶点剂量率为217．7cGy／min；0°静止照射时，Ф5mm、Ф40mm、625mm和Ф15mm准直嚣XZ平面的靶外剂量分布呈规律性变化，80％～20％的等剂量曲线为规则的圆形，而360°旋转照射时相应准直器YZ平面的靶外剂量分布的规律性发生改变。结论SRT系统的基本防护性能指标、准直器的大小与靶平面的方向直接影响靶外荆量分布。漏散射辐射对靶外刑量的贡献也不客忽视。

Objective To study the basic protective performance of SGS-1 stereotactic radiation treatment （SRT） system, the distribution of doses outside target and its infective factors, to design a comprehensive treat planning system （ TPS）, protect normal tissue and improve treatment effect. Methods A SGS-1 SRT system was used as the study object. Simultaneously, other test tools such as measure stick for focusing, films （MD-55 and Kodak）, spherical phantom, PTWUNIDOS dosimeter, LiF（ Mg, Cu,P） thermoluminescence dosimeter, DFS processing system of dose film were adopted. Results The error between mechardsm center and target center was 0.28 ram, doserate to the target was 217. 7 cGy/min. Besides these, the distribution of doses outside target changed regularly with the sizes of collimator （Ф755 mm,Ф40 mm,Ф25 mm orФ15 mm） , the directions of radiation plane （XZ or YZ） and the angles of radiation beams （0° -360°）. It was shown that the isodose curves from 80% to 20% were regular rounds when target plane was irradiated fixedly at 0° degree. Conclusion The distribution of doses outside target depends upon the basic protective performance of the treatment system, size of the collimator and the direction of target plane. Furthermore, the fact can＇t be ignored that a part of dose outside target comes from leakage radiation and scatter radiation.