直肠癌术前在无均整块器模式下容积弧形调强与固定野调强放疗计划的剂量学比较

Dosimetry comparison of volume-modulated intensity-modulated IMRT and fixed-field VMAT plans preoperative rectal cancer in the uniform monolithic mode

目的探讨瓦里安IX直线加速器使用6 MV的X射线在无均整块(Flatting-filter-free,FFF)模式下容积调强与固定野调强放疗计划的剂量学差异。方法选取2016年9月—2018年9月辽宁省肿瘤医院收治的53例直肠癌术前放疗患者做回顾性研究,每例患者在无均整块器模式下使用相同优化条件分别做容积弧形调强和固定野调强放疗计划。比较两种放疗计划中的靶区和危及器官的剂量学差异。结果靶区剂量方面,两种计划的靶区D2%、D98%、Dmean、CI和HI的差异有统计学意义。FFF-IMRT和FFF-VMAT计划相比较,D2%增大3.1%(P=0.001)、D98%减小4.5%(P=0.001)、Dmean减小2.4%(P=0.026)、CI减小(P<0.001)、HI增大(P=0.005)。危及器官方面,两种计划膀胱的D2%、Dmean、双侧股骨头的D2%、Dmean和骨盆的Dmean的差异有统计学意义。FFF-IMRT和FFF-VMAT计划相比较,膀胱的D2%增大2.7%(P<0.001)、Dmean减小20.4%(P<0.001),双侧股骨头D2%减小4.2%(P<0.001)、Dmean减小11.2%(P<0.001),盆骨Dmean减小8.9%(P<0.001)。而小肠的D2%和Dmean的差异无统计学意义(P>0.05)。FFF-IMRT的计划机器跳数为(978±127)MU,是FFF-VMAT的计划机器跳数(527±63)MU的1.86倍(P<0.001);FFF-IMRT的计划执行时间为(510±252.2)s,是FFF-VMAT的计划执行时间(232±52.5)s的2.21倍(P<0.001)。结论在无均整块模式下,容积弧形调强在靶区适形度和均匀度优于固定野调强放疗,且容积弧形调强治疗时间短,计划执行效率高,但固定野调强对于患者危及的器官做更好的保护。

Objective The aim of this study was investigate the dosimetric difference between VMAT and IMRT by VARIAN IX linear accelerator using 6 MV X-ray in flatting-filter-free mode.Methods A retrospective study was conducted on 53 patients with rectal cancer treated by preoperative radiotherapy in Liaoning Cancer Hispital from September 2016 to September 2018.Each patient in flatting-filter-free mode was used the same optimization conditions to perform VMAT and IMRT plans.The dosimetric differences were compared between target areas and organs in two modes of plans.Results In terms of target dose,there were statistically significant of differences in D2%,D98%,Dmean,CI and HI of the two plans.FFF-IMRT compared to FFF-VMAT,D2%increased by 3.1%(P=0.001),D98%decreased by 4.5%(P=0.001),Dmean decreased by 2.4%(P=0.026),CI decreased(P<0.001),and HI increased(P=0.005).In terms of organ at risk,there were statistically significant of differences in D2%,Dmean of bladder,D2%,Dmean of double femoral heads and Dmean of pelvis between the two plans.FFF-IMRT compared to FFF-VMAT,D2%of bladder increased by 2.7%(P<0.001)and Dmean decreased by 20.4%(P<0.001),D2%of double femoral head decreased by 4.2%(P<0.001),Dmean decreased by 11.2%(P<0.001),and Dmean of pelvis decreased by 8.9%(P<0.001).However,there was no significant of differences between D2%and Dmean of intestines(P>0.05).The planned machine hops of FFF-IMRT were(978±127)MU,which was 1.86 times of the planned machine hops of FFF-VMAT(527±63)MU(P<0.001).The planned execution time of FFF-IMRT was(510±252.2)s,which was 2.21 times that of FFF-VMAT(232±52.5)s(P<0.001).Conclusion In the flatting-filter-free mode,the conformity and uniformity of VMAT in target area are better than those of IMRT,the treatment time of VMAT was shorter and the execution efficiency of the plan was higher.However,IMRT could better protect the organs of patients.