不同束流模式对肺癌中等分割容积旋转调强放射治疗剂量学的影响

Dosimetry of Medium-Fractionated Volume Rotary Intensity Modulated Radiation Therapy for Lung Cancer with Different Beam Modes

目的:研究在肺癌中等剂量分割放射治疗中,不同束流模式对容积旋转调强(volumetric modulated arc therapy,VMAT)计划剂量学的影响,为临床束流模式的选择提供参考。方法:选取12例肺癌患者,均采用VMAT技术进行3个部分弧设计有均整器(flattening filter,FF)模式和无均整器(flattening filter free,FFF)模式两组治疗计划,比较两组计划的靶区和危及器官剂量学参数、跳数、机架最小旋转速度、优化时间。结果:两组ITVs[计划内靶区(internal target volume,ITVs)+转移淋巴结]的D_(98%)、D_(mean)、适形度指数(conformity index,CI)、均匀性指数(homogeneity index,HI)和计划靶区(planning target volume,PTV)的D_(98%)、HI剂量学参数的差异无统计学意义(P>0.05);ITVs的D_(2%)和PTV的D_(2%)、D_(mean)、CI剂量学参数的差异有统计学意义(P<0.05),FFF模式组ITVs的D_(2%)、D_(mean)均低于FF模式组,PTV的CI优于FF模式组。两组计划在双肺的V_(5)和健侧肺的V_(5)、D_(mean),心脏的V_(40)和V_(30),食管的D_(1cc)、V_(30)和气管的D_(1cc)、V_(30)、D_(mean),脊髓的D_(max),剂量学参数的差异无统计学意义(P>0.05);FFF模式组双肺的V_(30)、V_(20)、D_(mean)和患侧肺的V_(30)、V_(20)、V_(5)、D_(mean),心脏的D_(mean)低于FF模式且差异有统计学意义(P<0.05),但食管的D_(mean)高于FF模式组且差异有统计学意义(P<0.05)。FFF模式组跳数、机架最小旋转速度、优化时间均高于FF模式组且差异有统计学意义(P<0.05)。结论:两组计划均能满足临床要求,FFF模式对肺部的保护更好,尤其是患侧肺。FFF模式的跳数虽然高于FF模式,但机架最小旋转速度FFF模式更高,因此FFF模式执行效率更高。对于肺癌中等剂量分割治疗计划,可优先选择FFF模式。

Objective:To study the effect of different beam modes on planned dosimetry of volumetric modulated arc therapy(VMAT)in medium-dose fractionated radiotherapy for lung cancer.Methods:Twelve patients with lung cancer were selected,and three partial arc treatment plans were designed flattening filter(FF)model and flattening filter free(FFF)model using VMAT technology.The dosimetric parameters of target and organs at risk,monitor unit,minimum gantry rotation speed and optimization time obtained with the two plans were compared.Results:There were no significant differences in the dosimetry parameters of D_(98%)of ITVs[internal target volume(ITV)+lymph node metastasis],D_(mean),CI,D_(98%)of HI and PTV between the two groups(P>0.05).The difference in dosimetric parameters of D_(2%)of ITVs and D_(2%)of PTV,D_(mean) and CI were statistically significant(P<0.05).The D_(mean) and D_(2%)of FFF mode were lower than FF mode,while the CI of PTV mode was better than FF mode.The differences in the dosimetric parameters of the two lungs V_(5) and the healthy lung V_(5) and D_(mean),the heart V_(40) and V_(30),the esophagus D_(1cc),V_(30) and the trachea D_(1cc),V_(30) and D_(mean),and the spinal cord Dmax were not statistically significant(P>0.05).In FFF mode,V_(30),V_(20),D_(mean) of both lungs,V_(30),V_(20),V_(5),D_(mean) of the affected lung,and D_(mean) of the heart were significantly lower than those in FF mode and the difference(P<0.05),while D_(mean) of the esophagus was significantly higher than that in FF mode(P<0.05).Besides,the monitor unit,minimum rotation speed and optimization time in FFF mode were significantly higher than those in FF mode(P<0.05).Conclusion:Both models can meet the clinical requirements.FFF model has better protection for lungs,especially the affected lung.Although the monitor unit of FFF model is higher than that of FF model,the minimum rotation speed of the gantry is higher in FFF model,which guaranteed a higher execution efficiency for FFF model.The FFF model may be preferred for the medium-dose fractiation treatment plan for lung cancer.