统计学不确定度对非小细胞肺癌SBRT计划的影响

Impact of Statistical Uncertainty on Stereotactic Body Radiation Therapy Plan for Non-Small Cell Lung Cancer

目的:研究不同统计学不确定度(statistical uncertainty,SU)在X射线体素蒙卡算法(X-Ray Voxel Monte Carlo,XVMC)下,对于肺癌立体定向放射治疗计划(stereotactic body radiotherapy,SBRT)的结果影响。方法:使用医科达Monaco 5.11临床计划设计系统,在同台加速器实施,采用相同的计划函数配置条件和参数设置要求的情况下,分别采用每个计划0.5%、1%、3%、5%的SU值对肺癌SBRT病例进行计划设计,并对计划数据结果、剂量分布及XVMC算法中的特征数据进行统计分析。结果:SU值在0.5%~5%的变化中,PTVD95%和PTVDMAX逐步提高(P<0.05),SU1%~3%组间差异最大;危及器官受量以及靶区均匀性指数(conformity index,CI)受到影响较小(P>0.05);XVMC剂量计算时间(estimated total delivery time,ETT)SU 0.5%~1%差异最大300s以上,SU3%~5%无差异;粒子历史压缩模拟次数(history density,HD)SU0.5%~1%差异最大为199.4,SU3%~5%无差异;整体计划不确定度(dose uncertainty for the entire calculation,DUEC)极值差异-1.18;受到SU值提高的影响,剂量计算时长增加,参与模拟粒子密度降低,整体计划不确定度增加。不同SU值对于计划验证通过率和等中心点剂量影响不明显(P>0.05),但随SU值增大有降低趋势;110%以上剂量分布各组间差异明显,SU0.5%计划中分布体积最小。结论:对于肺癌SBRT计划,由于其单次剂量较高(一般单次处方剂量在5Gy以上)的特点,在可接受的时间成本下,应保证更高的计划验证通过率,本研究推荐在肺癌SBRT计划中使用0.5%,最大不超过1%的SU值。

Objective: To explore the effect of different statistical uncertainty（ SU） values on stereotactic body radiation therapy（ SBRT） plan for non-small cell lung cancer according to X-ray Voxel Monte Carlo. Methods: With the same planning function configuration conditions and parameter settings,the Elekta Monaco 5.11 treatment planning system（ MONACO TPS） was employed for SBRT planning for central NSCLC cases,using SU values of 0.5%,1%,3% and 5%,respectively. The treatment plans were delivered by the same accelerator.Results: As the values of SU changed from 0.5% to 5%,95% of planning target volume( PTVD95%) and maximum dose of PTV( PTVDmax) increased gradually（ P<0.05）; and when the values of SU ranged from 1% to 3%,the difference among groups was the greatest. The dose to the organs at risk and the conformity index of the target region were slightly affected（ P>0.05）. When the values of SU ranged from 0.5% to 1%,the maximum difference of history density and estimated total delivery time between groups were 199.4 and greater than 300 s,respectively. And no obvious difference was observed in SU when the degree was between 3% and 5%. Difference in extreme values of dose uncertainty for the entire calculation（ DUEC） was-1.18. As the values of SU rose,dose calculation time increased,particle density decreased,and uncertainty of the treatment program increased. SU values showed no significant effect on dosimetric verification passing rate and isocenter dose（ P>0.05）,but a downward trend with the increasement of SU values. Difference in dose distribution among groups was significant when the dose was higher than 110%,and the corresponding volume was the smallest when SU was 0.5%. Conclusion: Because the single dose prescribed in the SBRT program for lung cancer was more than 5 Gy,a higher pass rate of dosimetric verification results was needed if time is permitted. This study recommends the SU value of 0.5%（ with a maximum of no more than 1%） in the SBRT program for lung cancer.