基于周围型肺癌高剂量率无均整滤过器模式下的2种动态适形弧计划比较

Comparison of 2 dynamic conformal arc plans based on high-dose rate flattening filter free beams for peripheral lung cancer

目的:对高剂量率无均整滤过器模式下的2种动态适形弧计划进行比较,评价其剂量学上的差异。方法:选取20例早期周围型非小细胞肺癌患者,在Eclipse 10.0计划系统中分别设计基于肿瘤中心的动态适形弧(base tumor-center dynamic conformal arc,T-DCA)和基于等中心的动态适形弧(base iso-center dynamic conformal arc,Iso-DCA)计划。选择Truebeam加速器无均整滤过器6 MV X射线,剂量率为1 400机器跳数(monitor unit,MU)/min,处方剂量为4 800 cGy,1 200 cGy/次,分4次治疗。靶区覆盖和危及器官限量均按美国放射治疗肿瘤学组(Radiation Therapy Oncology Group,RTOG)标准进行设计,并对2种计划进行比较。结果:T-DCA和Iso-DCA计划的靶区剂量覆盖差异无统计学意义(P>0.05),均能满足RTOG对靶区的剂量要求。2种计划的适形指数(conformity index,CI)和均匀指数(homogeneity index,HI)差异均无统计学意义(均P>0.05),但是距离计划靶区2 cm处任意方向的最大剂量的百分数(D2 cm)和50%处方剂量的等剂量线所包绕的体积与计划靶区体积的比值(R50%)的差异均有统计学意义(均P<0.05)。Iso-DCA的MU较T-DCA增加了21%。在T-DCA和Iso-DCA计划的危及器官的剂量学参数中,除脊髓和食管的最大受照射剂量外,其余差异均无统计学意义(均P>0.05)。结论:Iso-DCA计划靶区外的剂量跌落优于T-DCA计划,但是T-DCA计划能更好地保护脊髓和食管,同时T-DCA计划的MU更少。

Objective: To compare 2 dynamic conformal arc plans based on the high dose rate flattening filter free(FFF) beams, and to evaluate the dosimetric differences.Methods: A total of 20 patients with early peripheral non-small cell lung cancer were selected, and 2 dynamic conformal arc plans were designed in the Eclipse 10.0 treatment planning system(TPS). One of them was based on tumor-center(T-DCA), and the other was based on iso-center(Iso-DCA). Both plans were created by using the Truebeam linear accelerator, based on 6 MV FFF photons with a dose rate at 1 400 monitor unit(MU)/min.All patients received the prescribed dose of 4 800 cGy in 4 fractions(1 200 cGy/fraction).Target coverage and organ at risk limits were planned and designed according to the Radiation Therapy Oncology Group(RTOG) Criteria, and were compared between the TDCA and the Iso-DCA plans.Results: There was no significant difference in the target coverage between the T-DCA and Iso-DCA plans(P>0.05). Conformal index and homogeneity index had no significant differences(both P>0.05), but the percentage of the maximum dose in any direction 2 cm away from the planned target area(D2 cm) and the ratio of the volume wrapped by the isodose line of 50% prescription dose to the volume of the planned target area(R50%)showed significant differences(both P<0.05). The MU of the Iso-DCA plan was increased by 21% compared with that of the T-DCA plan. Except the maximum dose of spinal cord and esophagus, there was no significant difference in the other dosimetric parameters of the organs at risk between the T-DCA and the Iso-DCA plans(all P>0.05).Conclusion: The dose fall-off of Iso-DCA plan is better than T-DCA plan, but the T-DCA plan is consistently superior in sparing dose to spinal cord and esophagus, and the T-DCA plan has fewer MU.