准直器角度对肺癌SBRT-VMAT治疗计划的影响

目的:研究准直器角度对中央型非小细胞肺癌(NSCLC)患者体部立体定向放射治疗(SBRT)容积旋转调强(VMAT)计划剂量学影响。方法:选取10名中央型NSCLC患者进行VMAT计划设计。使用Varian Eclipse系统,6 MV FFF X射线,最大剂量率1400 MU/min。机架角度:CCW 179°~181°、CW 181°~179°,双弧准直器角度互组,0°~90°每间隔10°设置准直器角度,即为(0°,0°)、(10°,350°)、(20°,340°)、(30°,330°)、(40°,320°)、(50°,310°)、(60°,300°)、(70°,290°)、(80°,280°)和(90°,270°)制定十个计划。在处方剂量相同并且处方剂量线包绕相同靶区体积的前提下(归一至80%),比较计划靶区参数:D 95%、V 90%、适形度指数(CI)、梯度指数(GI)、D 2 cm以及机器跳数(MU),危及器官参数:双肺(D 1500 cm³、D 1000 cm³)、心脏(D 15 cm³)、脊髓(D 1.2 cm³、D 0.35 cm³)。用SPSS软件对每个分析指标做Wilcoxon符号秩检验,判断差异是否具有统计学意义。结果:在有统计学意义的基础上,10组计划中,准直器角度为60°时(P<0.05),靶区D 95%剂量最高,准直器角度为50°时(P<0.05),靶区V 90%最高。CI和GI在0°最佳。危及器官双肺(D 1500 cm³、D 1000 cm³)、心脏(D 15 cm³)、脊髓(D 1.2 cm³)受照剂量均在0°最低,脊髓D 0.35 cm³在整个角度范围内不具有统计学差异。此外,所有计划中危及器官受照剂量均远远低于计划规定值,其中双肺(D 1500 cm³)在50°的剂量与最低值仅相差4.1%(P<0.05),心脏(D 15 cm³)在60°的剂量与最低值仅相差3.4%(P<0.05)。结论:改变准直器角度对肺癌SBRT-VMAT计划剂量有明显的影响。选择合适的准直器角度,正常组织受照剂量远远低于计划限量时,靶区体积剂量明显提高,但计划复杂度也略有提升。在临床计划设计过程中,应充分考虑准直器角度的影响,制定更合适的治疗计划。

Effects of collimator angle on stereotactic body radiation therapy-volumetric modulated arc therapy in lung cancer

Objective:To evaluate the effects of collimator angle on the dosimetric results of volumetric modulated arc therapy(VMAT)plan for patients with central non-small cell lung cancer(NSCLC)undergoing stereotactic body radiation therapy(SBRT)treatment.Methods:VMAT plans for 10 patients with central NSCLC were analyzed.Optimization was performed in Varian Eclipse.6 MV X-ray non-flattened(6FFF)and maximum dose rate of 1400 MU/min were used.We used two full coplanar arcs in all plans(CCW 179°~181°,CW 181°~179°)with collimator angle set to(0°,0°),(10°,350°),(20°,340°),(30°,330°),(40°,320°),(50°,310°),(60°,300°),(70°,290°),(80°,280°)and(90°,270°)in one arc and the counterangle for the other.Other constraints remained unchanged.D 95%,V 90%,conformal index(CI),gradient index(GI),MU for target PTV and D 1500 cm³,D 1000 cm³ for lung,D 15 cm³ for heart,D 1.2 cm³,D 0.35 cm³ for spinal cord were analyzed.Wilcoxon signed rank test was performed using SPSS.A P-value<0.05 was regarded as statistical significance.Results:The best value of D 95%and V 90%for PTV was at 60°and 50°respectively.The best value for CI,GI and lung,heart,D 1.2 cm³ for spinal cord were at 0°.There was no significant differences for D 0.35 cm³ of spinal cord.Besides,all OAR doses were significantly smaller than clinical constraints.D 1500 cm³ of lung at 50°(P<0.05)and D 15 cm³ of heart at 60°(P<0.05)were higher than the best value for 4.1%and 3.4%respectively.Conclusion:Collimator angle rotation significantly affects the dosimetric results.Choosing an appropriate collimator angle could dramatically increase the dose of target while the OAR doses meet the clinical requirements.However,the plan complexity may increase slightly.Therefore,collimator angle should be taken into consideration to obtain a more optimized treatment plan in our clinics.