全身集成定位架对放疗靶区吸收剂量的影响  

Effects of systemic integrated orientation frame on absorbed dose of target areas in radiotherapy

作　　者：洪君 单鹄声[1] 周玉凤 HONG Jun;SHAN Husheng;ZHOU Yufeng(Department of Radiotherapy,the 82nd Hospital of the PLA,Huai＇an 223001,China)

机构地区：[1]解放军第82医院放疗科,江苏淮安223001

出　　处：《中国医学物理学杂志》2018年第7期785-789,共5页Chinese Journal of Medical Physics

摘　　要：目的:研究YC-TQ-Ⅱ型全身集成定位架对放疗靶区吸收剂量的影响。方法:将尺寸为30cm×30cm×15cm的固体水模体固定在全身集成定位架体部中心轴上进行CT扫描后,将CT图像导入XiOTPS并勾画出固体水模体、靶区及全身集成定位架结构,之后以电离室为中心,机架角度从0°开始每隔一定角度添加一个10cm×10cm、100MU不同能量射线的照射野。考虑到高密度材料的大小对机架角度的影响,在以下机架角度范围内每隔1°测一个值(61°~79°、101°~119°、241°~259°、281°~299°);在其他机架角度范围内每隔10°测一个值(0°~60°、80°~100°、120°~240°、260°~280°、300°~350°)。根据对称性计算出高能X射线穿过全身集成定位架的衰减率,随后在医用直线加速器上用UNDOSE剂量仪进行同等条件下的测量来验证XiO TPS计算的准确性,最后在XiO TPS上对比有无全身集成定位架的三维适形放疗计划靶区吸收剂量变化情况。结果:全身集成定位架对高能X射线的最大衰减率为:13.0%(6MV)、11.4%(15MV),并且XiOTPS计算值与实际测量值符合得很好,最大偏差0.6%(15MV);添加全身集成定位架后靶区的D_(95%)由6000cGy变化为5304cGy(6MV)、5484cGy(15MV);放疗计划靶区的均匀性指数分别由0.091(6MV)、0.104(15MV)变化为0.195(6MV)、0.175(15MV);靠近体架端靶区的6000cGy、5500cGy等剂量线明显上移,且6MV比15MV严重。结论:YC-TQ-Ⅱ型全身集成定位架中的高密度材料可显著降低放疗靶区的吸收剂量,需要考虑其对高能X射线的衰减率并加以修正。Objective To discuss the effects of YC-TQ-Ⅱ systemic integrated orientation frame on the absorbed dose of target areas in radiotherapy. Methods A solid water phantom of 30 cm×30 cm×15 cm was fixed on the body center axis of systemic integrated orientation frame for CT scanning. Then the obtained CT images were imported into XiO TPS, and the solid water phantom, target areas and the structure of systemic integrated orientation frame were sketched. A 10 cm×10 cm and 100 MU radiation field with different energies at the center of ionization chamber was added at regular angels, which starting at 0°. Considering the effects of the size of high-density material on the angle, a value was measured at every 1° in the following angle ranges, namely 61°-79°, 101°-119°, 241°-259°, 281°-299°, and a value was measured at every 10° in other angle ranges（0°-60°, 80°-100°, 120°-240°, 260°-280°, 300°-350°）. According to symmetry, the attenuation rate was calculated when high-energy X-ray went through systemic integrated orientation frame. Then the accuracy of XiO TPS was verified by the measurement of UNDOSE dosimeter under the same conditions on medical linear accelerator. Finally, the changes of absorbed dose in three-dimensional conformal radiotherapy were analyzed on XiO TPS with or without systemic integrated orientation frame. Results The maximum attenuation rate of high-energy X-ray caused by systemic integrated orientation frame were 13.0%（6 MV）, 11.4%（15 MV）, and the calculated output of XiO TPS was in good agreement with measured value, with a maximum deviation of 0.6%（15 MV）. After adding systemic integrated orientation frame, the D_（95%） of target areas decreased from 6 000 cGy to 5 304 cGy（6 MV）, 5 484 cGy（15 MV）. The homogeneity index of target areas increased from 0.091（6 MV）, 0.104（15 MV） to 0.195（6 MV）, 0.175（15 MV）. The isodoses lined of 6 000,5 500 cGy of target areas closing to body frame were shifted up obviously, and the shift of 6 MV was m

关 键 词：集成定位架 放射治疗 衰减率 吸收剂量 

分 类 号：R811.1[医药卫生—放射医学]