肺密度变化对组织吸收剂量影响的模拟研究

摘要/Abstract

摘要： 为探究由呼吸运动引起的肺组织物理特性变化对肺组织及肿瘤组织吸收剂量的影响,基于蒙特卡罗方法进行模拟计算,使用EGSnrc(electron gamma shower software toolkit)程序将收集的不同密度肺组织数据转换成对应模体材料,建立不同呼吸状态下的组织模型,计算在不同射野照射下的百分深度剂量与离轴比差异,并探讨对目前常见照射技术的影响。结果表明,射野越小不同呼吸状态下组织吸收剂量差异越明显,在10 cm×10 cm射野下肺组织模体吸收剂量无明显差异,肿瘤模体吸收剂量最大降低3.86%;当射野小于5 cm×5 cm时上游肺组织模体吸收剂量随深度增加呈先增大后减小的趋势;在1 cm×1 cm时肺组织体膜吸收剂量差异最大达46.87%,肿瘤模体吸收剂量在1 cm×1 cm时差异最大达6.97%。同时在小野照射下低密度组织中存在明显的电子不平衡现象。在三维适形技术下呼吸运动引发的组织剂量差异小于调强及立体定向放射治疗,在呼吸门控技术下临床医生可结合TPS(treatment planning system)算法在吸气末进行靶区勾画,可降低正常肺组织剂量同时提高靶区剂量。

关键词: 呼吸, 肺组织, 密度, 剂量, 蒙特卡罗模拟

Abstract: To explore the effects of changes in the physical properties of lung caused by breathing exercise on the absorbed dose of lung and tumor, Monte Carlo method for simulation calculation using EGSnrc was used to convert the collected lung data of different densities into corresponding phantom materials, to establish tissue models under different breathing states, and to analyze the differences between PDD (percentage depth dose) and Profile under different radiation fields. Results showed that, the smaller the radiation field size, the more obvious the difference in tissue absorbed dose under different breathing states. There is no significant difference in lung absorbed dose under the 10 cm×10 cm radiation field, and the tumor absorbed dose is reduced by 3.86%. When the radiation field is smaller than 5 cm×5 cm, the absorbed dose of upstream lung increases first and then decreases with the increase of depth. When radiation field is 1 cm×1 cm, the maximum difference of lung absorbed dose is 46.87%, the tumor absorbed dose is reduced by 6.97%. At the same time, there is an obvious electron imbalance in low-density tissue under small radiation field. The difference in tissue dose caused by breathing exercise under 3D-CRT technology is smaller than IMRT and SBRT. Under breathing gating technology, clinicians can combine the TPS algorithm to delineate the target area at the end of inspiration, which can reduce the normal lung tissue dose and increase the target area dose.

Key words: breathe, lung, density, dose, Monte Carlo simulation

中图分类号:

R811.1

肖杨, 黄顺平, 李恒, 吴艳, 李进, 刘宏, 陈晓琳. 肺密度变化对组织吸收剂量影响的模拟研究[J]. 辐射防护, 2022, 42(4): 354-360.

XIAO Yang, HUANG Shunping, LI Heng, WU Yan, LI Jin, LIU Hong, CHEN Xiaolin. A simulation study on the influence on tissue dose caused by lung density change[J]. RADIATION PROTECTION, 2022, 42(4): 354-360.

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