周围型肺癌无均整滤过器模式SBRT的剂量学研究

Dosimetry study of SBRT of using flattening filter free beams for peripheral lung cancer

目的:评价动态适形拉弧(DCA)和容积旋转(RA)两种体部立体定向放射治疗(SBRT)技术在早期周围型非小细胞肺癌治疗中的剂量学差异。方法:选取15例早期周围型非小细胞肺癌患者,进行4D-CT扫描,按照美国放射治疗肿瘤学组(RTOG)标准勾画靶区和危及器官(OAR)。在Eclipse 10.0治疗计划系统中分别设计基于DCA技术和RA调强技术的体部立体定向放射治疗计划。采用TrueBeam加速器无均整滤过器6 MV X射线,剂量率为1400 MU/min,处方剂量为48 Gy,分4次治疗。计划设计中的靶区剂量覆盖和OAR限量要求均按RTOG标准执行。评价靶区90%、95%和100%处方剂量覆盖的体积(V_(90%)、V_(95%)和V_(100%))、适形性指数(CI)、均匀性指数(HI)、距离靶区2 cm处任意方向的最大剂量的百分数(D_(2cm))、50%处方剂量的等剂量线所包绕的体积与靶区体积的比值(R_(50%))、OAR受照剂量的最大值(D_(max))以及机器跳数及计划设计时间。结果:DCA和RA计划的靶区剂量覆盖的差异和OAR受照剂量的差异均无统计学意义,计划设计的要求均能满足RTOG标准。DCA和RA计划靶区的CI分别为1.45±0.16和1.06±0.02,差异有统计学意义(t=6.543,P<0.05),HI的比较差异无统计学意义。两种计划的D_(2cm)、R_(50%)、MU和计划设计时间比较差异均有统计学意义(t=6.267,t=8.151,t=6.037,t=6.316;P<0.05)。结论:DCA和RA计划对OAR的保护无差别,但RA计划的适形性优于DCA计划。DCA计划显著的降低了机器跳数和减少了计划设计时间。

Objective:To evaluate the dosimetric differences between two kinds of stereotactic body radiotherapy(SBRT)techniques for the early stage peripheral non-small cell lung cancer(NSCLC).Methods:Fifteen patients with early peripheral NSCLC were selected and underwent 4 dimensional computed tomography(4D-CT)scan.The target volumes and organs at risk(OAR)were delineated according to radiation therapy oncology group(RTOG)protocols.SBRT plans based on dynamic conformal arc(DCA)and Rapidarc(RA)were created respectively in the Eclipse 10.0 treatment planning system.All plans used TrueBeam accelerator with 6MV X-ray using flattening filter free beams with a dose rate of 1400MU/min.All patients received a prescription dose of 48 Gy given in 4 fractions.The target dose coverage and the requirement of limited dose of OAR were considered according to the RTOG constraints.In addition,the coverage volumes of target volume received 90%(V_(90%)),95%(V_(95%))and 100%(V_(100%))of the prescription dose,conformity index(CI),homogeneity index(HI),the percentage of maximum dose at 2 cm from the target region in all directions(D_(2cm)),the ratio of the wrapped volume of the isodose line of 50%of prescription dose to the volume of the target region(R_(50%)),the maximum value of the OAR exposure dose,monitor unit(MU)and the time of planned design were further evaluated.Results:There was no significant difference between DCA and RA plans for the dose coverage of target region and the difference of OAR exposure dose between DCA and RA was not significant.The requirements of planned designs could meet the RTOG criteria.The CIs of planned target region of DCA and RA were 1.45±0.16 and 1.06±0.02,respectively,and the difference of that between them was significant(t=6.543,P<0.05),while there was no significant difference in HI.The differences of D_(2cm),R_(50%),monitor units(MU)and planned design time between two kinds of plans were significant(t=6.267,t=8.151,t=6.037,t=6.316,P<0.05).Conclusion:There is no difference in protecting OARs between DCA plan and RA plan,but RA is significantly better than DCA for the CI.And DCA plan can significantly reduce MU and shorten the time of planned design.