食管癌术后纵隔淋巴结转移容积旋转调强与静态调强放疗的剂量学对比研究

目的比较容积旋转调强（volumetric modulated arc therapy，VMAT）与静态调强（intensity modulated radiotherapy，IMRT）放疗技术治疗食管癌术后纵隔转移淋巴结的剂量学差异。方法对25例胸段食管癌术后纵隔淋巴结转移患者分别设计逆时针VMAT计划和5野IMRT计划，在满足靶区处方剂量要求下，通过剂量体积直方图（DVH）评价和比较2种类型治疗计划的适形性指数（CI），均匀性指数（HI），脊髓最大剂量（Dmax）、V40（Vx为xGy剂量曲线包含相应器官体积百分数），双肺V5、V10V20、V30胸腔胃V40、V50、平均剂量（Dmean），心脏V40、V50、Dmean。并比较2种治疗计划总机器跳数（monitorunit，MU）和治疗时间。结果全组25例患者的VMAT计划和IMRT计划均能满足临床剂量学要求，在靶区覆盖率相似的前提下，VMAT计划靶区（PTV）CI优于IMRT计划，差异具有统计学意义（P〈0．05），HI差异无统计学意义（P〉0．05）。与IMRT计划相比，VMAT计划中双肺V5、V10有所上升，V20、V30明显降低（P〈0．05）；脊髓Dmax显著降低（P〈0．05）；胸腔胃V40、V50明显减少（P〈0．05）；心脏V30V40、Dmean略有上升趋势，但差异无统计学意义（P〉0．05）。结论VMAT靶区适形度更高，降低周围重要正常组织高剂量范围，这可能减少正常组织放疗反应，同时可通过降低MU和缩短实际治疗时间，提高肿瘤治疗效果。

A dosimetric comparison of VMAT and static IMRT to treat mediastinal metastasis from esophageal carcinoma after surgery

Objective To compare the dosimetric difference between volumetric modulated arc therapy （VMAT） and static intensity modulated radiotherapy （IMRT） when applied to treat mediastinal metastasis from esophageal carcino- ma after surgery. Methods A total of 25 patients diagnosed with mediastinal metastasis from esophageal carcinoma after surgery were included in the current study. VMAT plans with a single are and IMRT plans were designed for each pa- tient. Both plans were compared for conformal index （CI）, homogeneity index （HI）, spinal Dmax and V40; V5, V10, V20 and V30 in the lungs; V40, V50 and Dmean in the intrathoraeie stomach; and V40, V50 and Dmean in the heart through dose -volume histogram （DVH） , when sufficient doses were provided within targeted regions. The monitor units （MU） and treatment time （TT） were also evaluated. Results All plans designed for 25 patients could provide enough doses for clinical use. On the basis of similar coverage within the targeted regions, VMAT plans produced better CI than IMRT plans （ P 〈 0.05 ）, despite of little statistical difference in HI （ P 〉 0.05 ）. Compared with IMRT plans, VMAT reported increased V5 and V10 and remarkably declined V20 and V30 （ P 〈 0.05 ） in the lungs ; significantly lower spinal Dmax （ P 〈 0.05 ） ; reduced V40 and V50 in the intrathoraeic stomach （ P 〈 0.05 ） ; as slightly increased V30, V40 and Dmean in the heart. The average MU and treatment time of VMAT were reduced. Conclusion VMAT plans produce higher values of CI in the target regions and reduce the dose range surrounding normal tissues, which can be adopted to weaken the side effects within normal tissues and improve efficacy through reduction of MU and treatment duration.