Peripheral lung lesions treated with a single fraction of stereotactic ablative body radiotherapy (SABR) utilizing volumetric modulated arc therapy (VMAT) delivery and flattening filter‐free (FFF) beams represent a potentially high‐risk scenario for clinically significant dose blurring effects due to interplay between the respiratory motion of the lesion and dynamic multi‐leaf collimators (MLCs). The aim of this study was to determine an efficient means of developing low‐modulation VMAT plans in the Eclipse treatment planning system (v15.5, Varian Medical Systems, Palo Alto, USA) in order to minimize this risk, while maintaining dosimetric quality. The study involved 19 patients where an internal target volume (ITV) was contoured to encompass the entire range of tumor motion, and a planning target volume (PTV) created using a 5‐mm isotropic expansion of this contour. Each patient had seven plan variations created, with each rescaled to achieve the clinical planning goal for PTV coverage. All plan variations used the same field arrangement, and consisted of one dynamic conformal arc therapy (DCAT) plan, and six VMAT plans with varying degrees of modulation restriction, achieved through utilizing different combinations of the aperture shape controller (ASC) in the calculation parameters, and monitor unit (MU) objective during optimization. The dosimetric quality was assessed based on RTOG conformity indices (CI100/CI50), as well as adherence to dose–volume metrics used clinically at our institution. Plan complexity was assessed based on the modulation factor (MU/cGy) and the field edge metric. While VMAT plans with the least modulation restriction achieved the best dosimetry, it was found that there was no clinically significant trade‐off in terms of dose to organs at risk and conformity by reducing complexity. Furthermore, it was found that utilizing the ASC and MU objective could reduce plan complexity to near‐DCAT levels with improved dosimetry, which may be sufficiently robust to overcome the interplay effect.

中文翻译：

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针对单级肺SABR的稳健VMAT输送解决方案，利用FFF光束将剂量折衷最小化。

采用立体定向消融身体放疗（SABR），采用容积调制弧光治疗（VMAT）输送和展平无滤光片（FFF）光束治疗的周围性肺部病变，由于相互作用而在临床上具有明显的剂量模糊效应，可能是一种潜在的高风险方案在病变的呼吸运动和动态多叶准直器（MLC）之间。这项研究的目的是确定在Eclipse治疗计划系统（v15.5，Varian Medical Systems，Palo Alto，美国）中制定低调制VMAT计划的有效方法，以便在保持剂量学质量的同时将这种风险降至最低。该研究涉及19位患者，这些患者的内部目标体积（ITV）轮廓涵盖了肿瘤运动的整个范围，以及使用该轮廓的5毫米各向同性展开创建的规划目标体积（PTV）。每位患者创建了七个计划变体，每个变体都进行了缩放以实现PTV覆盖的临床计划目标。所有计划变更都使用相同的场布置，并且由一个动态共形电弧治疗（DCAT）计划和六个具有不同调制限制程度的VMAT计划组成，这些计划通过在计算参数中利用孔径形状控制器（ASC）的不同组合来实现，并在优化过程中监控广告单元目标。根据RTOG合格指数（CI100 / CI50）以及对我们机构临床使用的剂量-体积指标的遵守情况，对剂量学质量进行了评估。基于调制因子（MU / cGy）和场边缘度量评估了计划的复杂性。尽管具有最小调制限制的VMAT计划实现了最佳剂量学，但发现通过降低复杂性，在风险和顺应性器官的剂量方面并没有临床上的重大折衷。此外，还发现利用ASC和MU物镜可以通过提高剂量学将计划的复杂性降低到接近DCAT的水平，这可能足以克服相互作用的影响。