ITV versus mid-ventilation for treatment planning in lung SBRT: a comparison of target coverage and PTV adequacy by using in-treatment 4D cone beam CT
ITV versus mid-ventilation for treatment planning in lung SBRT: a comparison of target coverage and PTV adequacy by using in-treatment 4D cone beam CT
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DOI：
10.1186/s13014-020-01496-5
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发表时间：
2020-03-03
影响因子：
3.6
通讯作者：
Chajon, E.
中科院分区：
文献类型：
--
作者：
Bellec, J.;Arab-Ceschia, F.;Chajon, E.
背景：内靶容积（ITV）方法和中间通气（MidV）概念是自由呼吸下两种主要的呼吸运动管理策略。这项工作的目的是比较实际的治疗中的目标覆盖率在体积调制电弧治疗（VMAT）通过ITV为基础的和基于MidV的计划靶体积（PTV）提供，并提供知识，在选择最佳的PTV立体定向体放射治疗（SBRT）肺部病变。方法与材料32例肺癌患者采用VMAT技术治疗。对于每个部分，通过使用基于4维锥形束CT（4D-CBCT）的图像引导程序定位靶的平均时间加权位置。通过使用与VMAT输送同时采集的治疗中4D-CBCT图像（4D-CBCTin-treat），确定每个部分在治疗输送期间大体肿瘤体积（GTV）的精确相关位置。GTV是从每个部分的10个呼吸相位排序的4D-CBCT治疗数据集中的每一个中描绘的。我们将目标覆盖率定义为患者呼吸周期期间PTV内GTV的平均百分比。报告了使用剂量概率边界的基于MidV的PTV（PTVMidV）和使用5 mm（PTVITV +5 mm）、4 mm（PTVITV +4 mm）和3 mm（PTVITV +3 mm）各向同性边界的三种基于ITV的PTV的靶覆盖率和PTV。报告治疗中基线位移和靶运动幅度，以评价两个参数对靶覆盖的影响。结果共分析了100幅4D-CBCT治疗图像。PTVMidV、PTVITV +5 mm、PTVITV +4 mm和PTVITV +3 mm的平均靶区覆盖率分别为98.6%、99.6%、98.9%和97.2%。在至少90%的评价病例中，所有PTV边界导致每次治疗的目标覆盖率高于95%。与PTVITV +5 mm相比，PTVMidV、PTVITV +4 mm和PTVITV +3 mm的平均PTV分别降低了16%、19%和33%。结论：当使用基于4D-CBCT的图像引导实施VMAT时，基于ITV的方法（比常用的5 mm边缘更紧）仍然是基于MidV的方法的替代方法，可减少肺SBRT中的健康组织暴露。与PTVMidV相比，PTVITV +3 mm显著降低了PTV，同时仍保持了足够的治疗中靶区覆盖。
Background The internal target volume (ITV) approach and the mid-ventilation (MidV) concept are the two main respiratory motion-management strategies under free breathing. The purpose of this work was to compare the actual in-treatment target coverage during volumetric modulated arctherapy (VMAT) delivered through both ITV-based and MidV-based planning target volume (PTV) and to provide knowledge in choosing the optimal PTV for stereotactic body radiotherapy (SBRT) for lung lesions. Methods and materials Thirty-two lung cancer patients treated by a VMAT technique were included in the study. For each fraction, the mean time-weighted position of the target was localized by using a 4-dimensional cone-beam CT (4D-CBCT)-based image guidance procedure. The respiratory-correlated location of the gross tumor volume (GTV) during treatment delivery was determined for each fraction by using in-treatment 4D-CBCT images acquired concurrently with VMAT delivery (4D-CBCTin-treat). The GTV was delineated from each of the ten respiratory phase-sorted 4D-CBCTin-treat datasets for each fraction. We defined target coverage as the average percentage of the GTV included within the PTV during the patient's breathing cycle averaged over the treatment course. Target coverage and PTVs were reported for a MidV-based PTV (PTVMidV) using dose-probabilistic margins and three ITV-based PTVs using isotropic margins of 5 mm (PTVITV + 5mm), 4 mm (PTVITV + 4mm) and 3 mm (PTVITV + 3mm). The in-treatment baseline displacements and target motion amplitudes were reported to evaluate the impact of both parameters on target coverage. Results Overall, 100 4D-CBCTin-treat images were analyzed. The mean target coverage was 98.6, 99.6, 98.9 and 97.2% for PTVMidV, PTVITV + 5mm, PTVITV + 4mm and PTVITV + 3mm, respectively. All the PTV margins led to a target coverage per treatment higher than 95% in at least 90% of the evaluated cases. Compared to PTVITV + 5mm, PTVMidV, PTVITV + 4mm and PTVITV + 3mm had mean PTV reductions of 16, 19 and 33%, respectively. Conclusion When implementing VMAT with 4D-CBCT-based image guidance, an ITV-based approach with a tighter margin than the commonly used 5 mm margin remains an alternative to the MidV-based approach for reducing healthy tissue exposure in lung SBRT. Compared to PTVMidV, PTVITV + 3mm significantly reduced the PTV while still maintaining an adequate in-treatment target coverage.