网格精度对肝癌立体定向放射治疗计划的剂量学影响

Dosimetric effect of grid size on stereotactic radiotherapy for liver cancer

目的:研究不同网格精度对肝癌立体定向放射治疗(SBRT)计划的剂量学影响,为临床肝癌SBRT计划的设计提供合适的网格精度。方法:回顾性分析湖北省肿瘤医院2017~2020年间采用VMAT-SBRT治疗方式的肝癌患者10例,在相同函数配置和参数设置条件下,分别采用1.0、2.0、3.0、4.0、5.0 mm网格精度设计治疗计划。比较靶区D95%、D_(mean)、适形度指数、梯度指数,危及器官中肝脏D_(mean)、正常肝脏的V_(10)、V_(20)、V_(30),脊髓的Dmax以及计划的计算时间,分析在3%/3 mm和2%/2 mm标准下Gamma通过率。结果:采用Eclipse系统AAA算法下对网格大小进行更改,结果显示靶区D95%随着网格值增大呈下降趋势,GI随着网格值增大呈增长趋势;在D_(mean)和适形度指数上,网格值对其产生的影响未见显著差异;在危及器官保护方面,1.0 mm网格表现出更优异的计算结果;在计算时间方面,随着网格大小减小,剂量计算时间呈大幅度增长;在计划验证通过率方面,随着网格大小增大,两种标准(2%/2 mm和3%/3 mm)下的通过率不断减小。结论:随着计算网格大小的改变,靶区和危及器官的剂量受量以及计算时间和Gamma通过率都有不同程度的改变。综合计划剂量优化结果以及计算时间和验证通过率,建议在肝癌SBRT计划设计中使用2.0 mm大小的计算网格。

Objective To study the dosimetric effect of different grid sizes on stereotactic radiotherapy(SBRT)for liver cancer,thereby providing an appropriate grid size for SBRT planning.Methods A retrospective analysis was performed on 10 cases of liver cancer patients treated with VMAT-SBRT in Hubei Cancer Hospital from 2017 to 2020.With the same function and parameter settings,treatment plans were designed with grid size of 1.0,2.0,3.0,4.0 and 5.0 mm,respectively.The D95%,D_(mean),conformity index and gradient index of the target area,the D_(mean) of the whole liver,the V_(10),V_(20),V_(30) of normal liver,the Dmax of spinal cord and calculation time for planning were compared.Moreover,the Gamma passing rates for the criteria of 3%/3 mm and 2%/2 mm were compared.Results The grid size was changed by the AAA algorithm of Eclipse system,and the results showed that with the increase of grid size,the D95% of the target area had a downward trend,and gradient index tended to increase,but that the effects of grid size on D_(mean) and conformity index were trivial.In terms of organs-at-risk sparing,better calculation results were obtained with the grid size of 1.0 mm.The dose calculation time was increased greatly with the decrease of grid size;and the Gamma passing rates for both two criteria(2%/2 mm and 3%/3 mm)were decreases as the grid size increases.Conclusion Computational grid size has different effects on the doses delivered to target areas and organs-at-risk,calculation time and Gamma passing rate.Based on the comprehensive consideration on dose optimization,calculation time and verification passing rate,the grid size of 2.0 mm is recommended in the clinical planning of VMAT-SBRT for liver cancer.