Ⅲ期大体积肺癌不同容积调强放疗技术的研究

Evaluation of different volumetric一modulated arc therapy for the large planning target volume in T3 lung cancer

目的评价全弧射野容积调强和部分多弧射野容积调强两种不同方式用于Ⅲ期大体积肺癌肿瘤靶区治疗的优劣性,比较肿瘤靶区及危及器官的剂量学差异,分析物理剂量对靶区局部控制和周边器官放疗副反应的影响,选取肺癌临床最优放疗技术.方法选取浙江省肿瘤医院2016年6月至2018年5月确诊且进行放疗的Ⅲ期大体积肺癌患者13例,肿瘤计划靶区(PTV)体积中位值是550.9 cm^3(402.2~834.8 cm^3).利用RayStation v 4.5计划系统的RayArc模块分别为每例患者设计两种容积调强计划:双全弧射野容积调强(F-VMAT),6个部分弧形射野容积调强(P-VMAT).肿瘤PTV处方剂量均为6 000 cGy/30 f.在靶区达到处方剂量要求下,利用剂量体积直方图(DVH)及Clincal goal工具比较靶区剂量的均匀性及适形性,肺、心、脊髓等危及器官的物理剂量.且记录其总机器跳数(MU).结果两种计划在满足靶区剂量的同时都可以较好地保护危及器官.F-VMAT计划在剂量均匀性指数(HI)和机器跳数方面优于P-VMAT计划(t=-3.904,P=0.002).但对于心脏的V30、V40、平均剂量(Dmean),P-VMAT计划占明显优势[V30(20.6±10.4)%比(16.4±8.9)%,t=3.822,P=0.02;V40(14.6±7.5)%比(11.88±7.1)%,t=3.096,P=0.009;Dmean(1 442.9±651.2)cGy比(1 263.5±605.6)cGy,t=3.986,P=0.02],而且P-VMAT计划可以显著降低肺的低剂量区域[V5(51.31±5.36)%比(43.44±5.28)%,t=6.908,P=0.00;V10(38.34±3.26)%比(34.05±3.74)%,t=4.632,P=0.001;Dmean(1 449±117.19)cGy比(1 375.38±148.98)cGy,t=4.93,P=0.00],两者对于肺的V20、V30及脊髓的Dmax差异均无统计学意义(均P>0.05).结论部分弧形射野容积调强用于Ⅲ期大体积肺癌肿瘤靶区治疗时,虽然比全弧射野容积调强需花费更多的治疗时间,但其给予肿瘤靶区充分的物理治疗剂量同时能更好的降低心脏和肺的部分受量,建议临床治疗可优先考虑规避重要器官的部分弧形射野容积调强计划.

Objective To investigate the feasibility and dosimetric characteristics of using dual - arc volumetric modulated arc therapy and multiple partial-arc VMAT for T3 lung cancer.Methods From June 2016 to May 2018,thirteen lung cancer patients with large planning target volume were replanned with dual full arcs VMAT (F-VMAT) and six partial-arc s VMAT( P-VMAT) on RayStation v4.5 RayArc function.PTV volume median was 550.9cm3(ranged 402.2-834.8cm3 ) and to a prescribed dose of 60 Gy in 30 fractions.Equivalent target coverage was required for all plans,and clinical goals were evaluated using various dose-volume metrics.These included PTV dose conformity,mean lung/heart dose,lung V5 ,V10 ,V20 ,V30 ,heart V30 and V40 ,and Dmax of spinal canal.The total monitor units ( MUs) were also examined. Results All VMAT plans satisfied the treatment criteria. F - VMAT achieved better homogeneity index ( HI) and MUs than P -VMRT( t = -3.904,P =0.002),and the conformal number(CN) of tumor volumes was likely clinically indistinguishable.However,F-VMAT significantly reduced lung V5 ,V10 and mean lung dose[V5:(51.31 ± 5.36)% vs.(43.44 ± 5.28)%,t=6.908,P=0.00;V10:(38.34 ± 3.26)% vs.(34.05 ± 3.74)%,t=4.632,P=0.001;Dmean:(1 449 ± 117.19)cGy vs.(1 375.38 ± 148.98)cGy, t=4.93, P =0.00 ], and heart dosimetric parameters were also observed in favor of P - VMRT [ V30 : (20.6 ± 10.4)% vs.(16.4 ± 8.9)%,t =3.822,P =0.02;V40:(14.6 ± 7.5)% vs.(11.88 ± 7.1)%,t =3.096,P =0.009;Dmean:(1 442.9 ± 651.2)cGy vs.(1 263.5 ± 605.6)cGy,t=3.986,P=0.02],and there were no statisti-cally significant differences in lung V20,V30 and spinal cord Dmax between the two groups(all P>0.05).Conclusion VMAT is an effective treatment for stage T3 lung cancer patients. The primary advantage of P - VMAT was the reduction in low dose area and decreased risk of symptomatic radioactive lung injury.It may be a priority for pulmonary malignancy patients with the large planning target volume.