双侧乳腺癌术后IMRT与VMAT的剂量学差异

Dosimetric differences between IMRT and VMAT for bilateral breast cancer in postmastectomy radiotherapy

目的:对比双侧乳腺癌术后放疗的不同治疗技术下靶区及危及器官的剂量学差异,探讨最佳治疗方案。方法:选择8例接受根治或者改良根治手术后的双侧乳腺癌患者,利用三维适形调强治疗系统为每例患者设计两种放疗方案。IMRT方案:设计10个野照射;VMAT方案:双侧胸壁同时进行两个Arc双弧照射。根据DVH图得出PTV的D_(mean)、V_(95)%、V_(107)%、V110%,靶区适形度指数(CI)、均匀性指数(HI)及正常组织(肺和心脏)受量体积差异来比较两种治疗技术。结果:两种治疗技术均能满足处方需求。靶区覆盖率都归至95%时,IMRT计划中PTV的Dmean优于VMAT计划中靶区的Dmean(P=0.04)。但是VMAT计划的V95%比IMRT提高了2.7 cm3(P=0.02),而V107%和V110%分别减少了2.93和0.05 cm^3,变化具有统计学差异(P=0.03, 0.03)。而且,在计划HI和CI方面,VMAT计划比IMRT计划更好(P=0.03, 0.05)。危及器官肺的参数:相较于VMAT计划,除了V5高于IMRT计划以外,其余参数均低于IMRT计划;而心脏的参数VMAT除了V_(40)以外其他的所有参数均高于IMRT计划,但是变化不具有统计学差异(P>0.05)。结论:相较于IMRT技术,VMAT计划靶区剂量分布更均匀,靶区和肺等受量优于IMRT计划,心脏的受量差于IMRT技术,但是仍在可接受范围内。因此,对于根治术后的双侧乳腺癌患者,使用VMAT双弧计划设计能获得较好的治疗收益。

Objective To compare the dosimetric differences of target areas and organs-at-risk between volumetric modulated arc therapy(VMAT) and intensity-modulated radiotherapy(IMRT) plans for bilateral breast cancer in postmastectomy radiotherapy,and discuss the optimal treatment scheme. Methods A total of 8 patients receiving radical or modified radical mastectomy for bilateral primary breast cancer were enrolled in this study. Three-dimensional conformal radiotherapy system was used to design two radiotherapy plans, namely IMRT and VMAT, for each patient. There were 10 fixed fields in IMRT plan. In VMAT plan,the bilateral chest wall was treated with double-arc VMAT. The dosimetric parameters obtained by dose-volume histogram,including the mean dose, V95%, V107%, V110%, conformity index and homogeneity index of planning target volume(PTV), and the dosimetric parameters of normal tissues, such as lungs and heart, were compared between two plans. Results Both the two plans met the prescription requirements. When the target coverage reached 95%, the mean dose of PTV in IMRT plan was better than that in VMAT plan(P=0.04). Compared with those in IMRT plan, the V95%of PTV in VMAT plan was increased by 2.7 cm3(P=0.02), while the V107%and V110%of PTV were decreased by 2.93 and 0.05 cm3, respectively(P=0.03, 0.03). Moreover, VMAT plan was superior to IMRT plan in the homogeneity index and conformity index(P=0.03, 0.05). The V5 of lungs in VMAT plan was higher than that in IMRT plan, while the other parameters of lungs in VMAT plan were lower than those in IMRT plan. Except the V40 of heart, the dosimetric parameters of heart in VMAT plan were higher than those of IMRT, without statistical differences(P>0.05). Conclusion VMAT plan is superior to IMRT plan in dose distribution and the dosimetric parameters of target areas and lungs. Although the dose of heart in VMAT plan is inferior to that in IMRT plan, the differences are still within acceptable range. Therefore, the patients receiving radical surgery for bilateral breast cancer can benefit more from double-arc VMAT.