气腔存在和小野条件下不同光子剂量算法的计算精度比较  

Comparison of Calculation Precision of Photon Dose between the Two Algorithms for the Situation with Air Cavity and Small Fields

作　　者：杨振[1] 胡逸民[2] 魏瑞[1] 

机构地区：[1]中南大学湘雅医院肿瘤科,长沙410008 [2]中国医学科学院肿瘤医院放疗科,北京100021

出　　处：《生物医学工程学杂志》2012年第1期75-79,共5页Journal of Biomedical Engineering

摘　　要：为了评估放射治疗剂量计算最常用的笔形束(PB)算法、卷积叠加(CS)算法处理小野且气腔存在条件下的计算精度,建立一包含气腔的水模体,分别用PB算法、CS算法和蒙特卡罗(MC)模拟计算1cm×1cm～7cm×7cm射野条件下该模体中的深度剂量和离轴比,并以MC模拟为标准比较深度剂量和离轴比曲线的扩展半影(自定义为10%～90%等剂量线之间的宽度)。研究结果显示PB算法和CS算法均高估了深度剂量,相比之下PB算法高估的程度更严重;CS算法计算的离轴比和MC模拟接近,向两侧发散,而PB算法计算的离轴比无明显发散。这表明在小野且气腔存在的情况下,PB算法和CS算法的计算精度都不高,但相对来说CS算法的计算精度高于PB算法。In order to evaluate the calculation precision of the pencil beam（PB） algorithm and convolution-superposition（CS） algorithm for the situation with air cavity and small fields,we built a water phantom with an air cavity slab,in which the depth dose（DD） and off-axis ratio（OAR） for field 1cm×1cm to field 7cm×7cm were calculated by PB algorithms,CS algorithms and Monte Carlo（MC） simulation.The evaluation of algorithms by MC simulation was achieved by comparisons of DD with the spread penumbras of OAR curve self-defined as the width between isodose lines of 10% and 90%.It was shown that PB algorithm and CS algorithm both overestimated the DD but the degree overestimated by PB algorithm was more serious.The CS algorithm showed a better agreement with the MC simulation for the OARs,which spread to both laterals,while that was not predicted accurately by PB algorithm.It was indicated that PB algorithm and CS algorithm do not have high calculation precision whereas CS algorithms is relatively better for the situation with air cavity and small fields.

关 键 词：笔形束算法 卷积叠加算法 蒙特卡罗模拟 等效组织空气比法 

分 类 号：R815[医药卫生—放射医学]