切向双弧容积弧形调强技术对保乳术后包括内乳淋巴结区照射的心脏剂量学评价

Cardiac dosimetric evaluation of tangential VMAT technique in patients with left breast cancer after breast-conserving surgery, including internal mammary lymph node irradiation

目的 通过对左侧乳腺癌保乳术后患者内乳淋巴结局部放疗，探讨一种新的切向50°双弧容积弧形调强放射治疗（tangential volumetric modulated arc therapy，T-VMAT）技术的剂量学特点，评价T-VMAT对心脏的潜在保护作用。方法 15例左侧乳腺癌保乳术后患者，每例患者分别设计常规加楔形板切线野（W-TF）、6野调强适形放射治疗（6F-IMRT）和T-VMAT计划，靶区处方剂量50 Gy/25次，计算并比较靶区和危及器官（OAR）的剂量体积参数和适形指标。结果 与W-TF相比，T-VMAT技术不仅可降低心脏和冠状动脉前降支（LAD）最大剂量Dmax、平均剂量Dmean和≥ 10 Gy剂量区体积（P〈0.05），而且有降低5 Gy剂量区体积V5 Gy趋势，但差异无统计学意义（P〉0.05）；与6F-IMRT相比，T-VMAT技术可明显降低心脏的Dmean、V5 Gy、V10 Gy和V20 Gy，以及LAD的Dmean、V5 Gy和V10 Gy（P〈0.05）。与W-TF相比，T-VMAT计划中同侧肺V20 Gy和健侧乳腺V5 Gy均未增加，差异无统计学意义（P〉0.05），且靶区剂量覆盖和适形度均明显优于W-TF，热点体积V110明显低于W-TF（P〈0.05）。结论 在不增加同侧肺和健侧乳腺受照体积的同时，T-VMAT不仅可以降低心脏和LAD高剂量区受照体积，而且有降低心脏和LAD低剂量区受照体积的趋势。

Objective To investigate the potential heart sparing effects of tangential volumetric modulated arc therapy （T-VMAT） by comparing its dosimetric properties with conventional wedged tangential fields （W-TF） technique and 6-field intensity-modulated radiotherapy （6F-IMRT） in the loco-regional radiotherapy of left breast cancer after conserving surgery, including internal mammary nodal irradiation. Methods Fifteen patients with left breast cancer were enrolled in this study. Three plans were generated for each patient：W-TF, 6F-IMRT and T-VMAT with two arc segments of 50°. The prescription dose to planning tumor volume （PTV） was 50 Gy in 25 fractions. Dose-volume parameters and indices of conformity were calculated and compared for the PTV and organs at risk （OAR）. Results Compared with W-TF, T-VMAT not only significantly decreased Dmax, Dmean and the high dose areas （above 10 Gy） of the heart and left anterior descending branch （LAD） （P〈0.05）, but also had the trend of sparing the V5 Gy although there was statistically significant difference （P〉0.05）. T-VMAT also significantly decreased Dmean, V5 Gy, V10 Gy and V20 Gy of the heart, as well as the Dmean, V5 Gy and V10 Gy of LAD （P〈0.05）, compared to 6F-IMRT. Furthermore, T-VMAT did not result in higher V20 Gy of ipsilateral lung and higher V5 Gy of contralateral breast compared with W-TF （P〉0.05）. T-VMAT achieved distinctly better target coverage and conformity, meanwhile obviously lowered hot volume of V110 compared to W-TF （P〈0.05）. Conclusions T-VMAT not only significantly decreased the high dose areas, but also had the trend of sparing the low dose area for the heat and LAD. Moreover, there was no significant difference for V20 Gy of ipsilateral lung and V5 Gy of contralateral breast between T-VMAT and W-TF.