CT造影剂对脑动静脉畸形VMAT计划剂量分布的影响

Effects of CT contrast agent on dose calculations for volumetric modulated arc therapy of brain arteriovenous malformations

目的:探讨CT造影剂对脑动静脉畸形VMAT计划剂量分布的影响。方法:选取15例脑动静脉畸形患者为研究对象,在相同体位下行平扫和增强CT扫描。在增强CT图像上勾画靶区和危及器官,通过图像配准将上述结构复制至平扫CT图像。在VARIAN Eclipse 13.6计划系统中完成增强CT图像的VMAT计划设计(5条弧),并将此计划复制至平扫CT图像,不进行通量优化,重新计算剂量分布。记录两组计划的靶区、危及器官以及感兴趣区域的CT值,靶区的D2%、D98%、Dmean、适形度指数、均匀性指数以及梯度跌落指数,危及器官Dmax以及正常组织受照射体积V2 Gy、V10 Gy、V12 Gy,并采用非参数配对Wilcoxon检验分析两组数据间的差异。结果:在靶区和感兴趣区域处,增强图像的CT值显著高于平扫图像(P=0.001);而在其他组织处,两组图像的CT值比较均无统计学差异(P>0.05)。两组计划的剂量学参数差异小于2%,且无统计学差异(P>0.05)。结论:CT造影剂对脑动静脉畸形VMAT计划剂量分布的影响较小,临床上可忽略。

Objective To investigate the effects of CT contrast agent on the dose calculations for volumetric modulated arc therapy(VMAT)of brain arteriovenous malformations.Methods Fifteen patients with brain arteriovenous malformations were enrolled in the study and underwent contrast enhanced CT(CECT)scan and non-enhanced CT(NECT)scan in the same position.Target areas and organs-at-risk were delineated on CECT image,and then copied to NECT image after image registration.VARIAN Eclipse planning system 13.6 was used to generate VMAT plan with 5 arcs based on CECT,and the generated plan was copied to NECT for recalculating dose distributions,without flux optimization.The Hounsfield unit(HU)of planning target volume,organs-at-risk and region of interest,the D2%,D98%,Dmean,conformity index,homogeneity index and gradient index of planning target volume,the Dmax of organs-at-risk,and the V2 Gy,V10 Gy and V12 Gyof normal tissues were recorded and analyzed.A Wilcoxon signed rank test was conducted to compare the differences between two groups of data.Results The HU of planning target volume and region of interest in CECT were higher than those in NECT(P=0.001),and there was no significant difference in HU of other tissues(P>0.05).The differences in dosimetric parameters between two groups were less than 2%,without significant differences(P>0.05).Conclusion The effect of CT contrast agent on the dose calculation for VMAT of brain arteriovenous malformations is ignorable.