小野照射不同密度肺模体横向电子不平衡现象的蒙特卡罗模拟研究
Monte Carlo simulation of lateral electron disequilibrium in different lung density phantoms after small-field radiation

李洁 ^1,2 汪晖 ¹ ^* 汪冬 ¹ 郑华庆 ¹ 吴宜灿 ¹

文摘	目的:研究小野对不同密度肺模体横向电子不平衡程度的影响,为肺部小野放射治疗提供参考.方法:利用蒙特卡罗程序EGSnrc/DOSXYZnrc对不同射野照射包含不同密度肺组织的模体进行模拟,选择6和15 MV两种能量、8种射野大小[(0.2×0.2)cm~2~(3.0×3.0)cm~2]、7种肺密度(0.001~1.000 g/cm~3)的不同组合,利用剂量衰减百分比(DRP)衡量横向电子不平衡的严重程度.结果:当肺密度小于0.4 g/cm~3时,DRP非常大且随密度剧烈变化,电子不平衡现象比较严重;当肺密度大于0.4 g/cm~3时,DRP随密度变化幅度减缓.肺内剂量衰减程度随射野的增加而减小,肺组织后方相对更小的野会有较大程度的剂量升高.结论:低密度范围内,密度的改变会引起肺部剂量的剧烈变化,在使用小野对肺部肿瘤进行治疗时,应更加注意CT-电子密度转换曲线的准确性,谨慎选择放射治疗参数以保护肺周围重要危及器官.针对低密度肺的剂量计算,应选用考虑电子不平衡的更精确的剂量计算方法.
其他语种文摘	Objective To study the effects of small-field radiation on lateral electron disequilibrium in different lung density phantoms and provide references for small-field radiotherapy for lung cancers. Methods Monte Carlo code EGSnrc/DOSXYZnrc was used to simulate different densities of lung tissues after radiation with different field sizes. The combinations of 2 kinds of energies (6 MV and 15 MV), 8 kinds of field sizes (from 0.2 cm×0.2 cm to 3.0 cm×3.0 cm) and 7 kinds of lung densities (from 0.001 g/cm~3 to 1.000 g/cm~3) were selected in the simulation. The lateral electron disequilibrium was evaluated by dose reduction percentage. Results The dose reduction percentage was very large and changed remarkably with the density when the lung density was less than 0.4 g/cm~3. However, when the lung density was greater than 0.4 g/cm~3, the change of dose reduction percentage was mitigated with the density. The attenuation of lung dose decreased with the increase of radiation field, and the doses in the small fields behind the lung tissues were significantly increased. Conclusion In a range of low density, the change of density might cause dramatic changes in the lung dose. During the treatment for lung cancer, medical physicists should pay more attention to the accuracy of the CT- electron density conversion curves and select the optimal radiotherapy parameters to protect the organsat- risk around the lungs. A more accurate dose calculation method considering the electron disequilibrium is recommended in the low-density lung dose calculation.
来源	中国医学物理学杂志 ,2019,36(4):379-383 【扩展库】
DOI	10.3969/j.issn.1005-202X.2019.04.002
关键词	小野 ; 肺密度 ; 放射治疗 ; 电子不平衡 ; 蒙特卡罗模拟
地址	1. 中国科学院核能安全技术研究所, 中国科学院中子输运理论与辐射安全重点实验室, 安徽, 合肥, 230031 2. 中国科学技术大学科学岛分院, 安徽, 合肥, 230026
语种	中文
文献类型	研究性论文
ISSN	1005-202X
学科	基础医学;特种医学
基金	国家自然科学基金 ; 中国科学院合肥物质科学研究院院长基金
文献收藏号	CSCD:6478567