动态容积调强放疗技术应用于老年低位直肠癌根治性放疗的剂量学研究

Dosimetric study of VMAT for definitive radiotherapy of elderly patients with low rectal cancer

目的:比较老年低位直肠癌行根治性放疗应用7野静态调强放疗(7F-IMRT)与动态容积调强放疗(VMAT)两种计划的剂量学差异。方法:应用Pinnacle 9.0治疗计划系统分别对21例行根治性放化疗的老年低位直肠癌患者进行7F-IMRT和VMAT两种计划设计,应用剂量体积直方图(DVH)比较分析两种放疗技术的靶区剂量分布特点和危及器官的受照射剂量和体积。结果:7F-IMRT和VMAT计划均能满足计划设计要求,VMAT与7F-IMRT的适形性指数(CI)分别为1.16和1.22,VMAT适形性优于7F-IMRT(P<0.05);均匀性指数(HI)分别为0.07和0.08,VMAT比7F-IMRT均匀性好,但差异无统计学意义(P>0.05)。在危及器官剂量中,VMAT技术使膀胱在低剂量及高剂量受累体积上均低于7F-IMRT技术。对于肠道VMAT增加了中剂量区V_(30)和V_(40),但减少了低剂量区V_(15)和高剂量区V_(50)受累体积。两组计划中双侧股骨头受量的指标D_(mean)、V_(30)、V_(50)差异均无统计学意义。VMAT计划与7F-IMRT计划的平均加速器跳数(MU)分别为372.20和528.06(P<0.05);两种计划平均治疗时间分别为169 s和410 s(P<0.05)。结论:VMAT计划具有降低总MU、缩短治疗时间及减少膀胱及小肠受照射剂量的优势,从而减轻患者放疗不良反应。

Objective:To compare the dose difference between volumetric modulated arc therapy(VMAT) and 7F-ntensltymodulated radiation therapy(7F-IMRT) in definitive radiotherapy for elderly patients with low rectal cancer.Methods:Twenty-one patients with low rectal cancer conducted definitive radiotherapy were selected with Pinnacle 9.0.VMAT and 7F-IMRT plans were respectively designed for each patient.Dose-volume histogram was applied to compare the dose distribution of target volumes and OARs.Results:Intensity modulated radiation therapy 7F-IMRT and VMAT programs can meet the design requirements of the plan.The conformality index (CI) of VMAT and 7F-IMRT were 1.16 and 1.22 respectively.The conformability of VMAT is better than IMRT ( P <0.05).The uniformity index (HI) is 0.07 and 0.08 respectively.The uniformity of VMAT is better than IMRT.The difference was not statistically significant ( P >0.05).In the compromised organ dose,the low and high dose affected volume of VMAT technology was lower than IMRT technology.For the intestinal VMAT increased the medium dose area V 30 and V 40 ,the V 15 and V 50 of small intestine in VMAT plans were lower than that in 7F-IMRT plans.The Dmean,V 30 and V 50 of bilateral femoral head were no significant differences between two plans.The monitor unit of VMAT was significantly lower than that of 7F-IMRT plans (372.20 vs 528.06, P <0.05).Compared with 7F-IMRT plans,VMAT plans showed shorter treatment time (169s vs 410s, P <0.05).Conclusion:Compared with 7F-IMRT plans,VMAT plans have better HI and CI,with obvious advantages in protecting bladder and small intestine.The treatment time and control points are lower in VMAT plans.