有无Auto flash优化时摆位误差对乳腺癌容积旋转调强放疗计划剂量学的影响

Dosimetric study on positioning error of breast cancer VMAT plan with or without autoflash optimization

目的:探讨有无Auto flash参与优化时,不同方向的摆位误差对乳腺癌VMAT计划的剂量学影响。方法:选取20例行VMAT技术照射的右侧乳腺癌根治术后患者。Monaco治疗计划系统在优化时可以选择是否对靶区采用Auto flash虚拟外放多叶光栅边界进行优化,对治疗时Auto flash参与优化的计划,制定一个无Auto flash的计划,对于治疗时无Auto flash参与优化的计划,制定一个有Auto flash的计划。2个计划的优化函数和条件均保持一样。对制定好的计划在头脚、上下、左右6个方向上分别引入3 mm和5 mm的摆位误差,重新计算剂量分布,以PTV的V100,D98,D2,Dmean,患侧肺的V20、V5,健侧肺的V5,脊髓的Dmax以及心脏的Dmean的变化幅度评价治疗计划对摆位误差的敏感性。结果:对3 mm的摆位误差,有Auto flash优化的VMAT计划在任一方向上PTV的剂量偏差均小于5%,无Auto flash优化的VMAT计划在下方向上的PTV剂量偏差大于5%,其余均小于5%。对5 mm的摆位误差,有Auto flash优化的VMAT计划在左和下方向的PTV剂量偏差大于5%,其余均小于5%,无Auto flash优化的VMAT计划在左和下方向的PTV剂量偏差大于5%,其余均小于5%。但就偏差的幅度而言,有Auto flash的计划小于无Auto flash的计划。结论:有Auto flash的计划,在有摆位误差时剂量学差异小于无Auto flash的计划,在制定乳腺癌计划时应该采用Auto flash参与优化。两种计划均在内、上、前这三个方向上剂量学偏差最小,外、下、后三个方向上剂量学偏差最大,在摆位时更应该刻意关注。

Objective:To investigate the dosimetric effect of setting errors in different directions on the breast cancer VMAT plan when Autoflash is involved in optimization.Methods:Selected 20 patients after radical mastectomy of breast cancer who underwent VMAT technology irradiation in our hospital.The Monaco treatment planning system can choose whether to use Autoflash virtual external MLC boundary to optimize the target area during optimization,and develop a plan without Autoflash during treatment.Make a plan without Autoflash for the plan with Autoflash participating in optimization during the treatment,and vice versa.The optimization functions and conditions of the two plans remain the same.Introduce the positioning error of 3mm and 5mm in the six directions of head,foot,up and down,and left and right respectively for the prepared plan,and recalculate the dose distribution,using V100,D98,D2,Dmean of PTV,and V20,V5 of the affected lung./Dmean,the V5 and Dmean of the contralateral lung,the Dmax of the spinal cord,and the Dmean of the heart change the range to evaluate the sensitivity of the treatment plan to setup errors.Results:for 3mm setup error,the dose deviation of PTV was less than 5%for Auto flash-optimized VMAT in either direction,and more than 5%for non-Auto flash-optimized VMAT in the lower direction,the rest were less than 5%.For the setting error of 5 mm,the dose deviation of PTV in the left and lower directions of VMAT plan optimized by Auto flash is more than 5%,and the rest is less than 5%,no Auto flash optimization of the VMAT plan in the left and lower direction of the PTV dose deviation of more than 5%,the rest are less than 5%.However,in terms of the magnitude of deviation,plans with Auto flash are smaller than those without Auto flash.Conclusion:the plan with Autoflash,the dosimetric difference is smaller than the plan without Autoflash when there is a setup error,and Autoflash should be used to participate in the optimization when formulating the breast cancer plan.Both plans have the least sensitivity in the inner,upper,and first directions,and the most sensitive in the outer,lower,and rear directions,and they should be deliberately paid attention to when setting up positions.