Han Bin, Wu Bian, Hu Fala, Ma Yangguang, Wang Haiyang, Han Xinwei, Liu Gang, Guo Yuexin
The First Affiliated Hospital of Zhengzhou University, Henan, Zhengzhou, China.
Cancer Center, Union Hospital, Huazhong University of Science and Technology, Tongji Medical College, Wuhan, China.
Front Oncol. 2022 Dec 8;12:1010411. doi: 10.3389/fonc.2022.1010411. eCollection 2022.
The purpose of this study was to investigate the target dose discrepancy caused by intrafraction variation during stereotactic body radiotherapy (SBRT) for lung cancer.
Intensity-modulated radiation therapy (IMRT) plans were designed based on average computed tomography (AVG CT) utilizing the planning target volume (PTV) surrounding the 65% and 85% prescription isodoses in both phantom and patient cases. Variation was simulated by shifting the nominal plan isocenter along six directions from 0.5 mm to 4.5 mm with a 1-mm step size to produce a series of perturbed plans. The dose discrepancy between the initial plan and the perturbed plans was calculated as the percentage of the initial plan. Dose indices, including for internal target volume (ITV) and gross tumor volume (GTV), were adopted as endpoint samples. The mean dose discrepancy was calculated under the 3-dimensional space distribution.
We found that motion can lead to serious dose degradation of the target and ITV in lung SBRT, especially during SBRT with PTV surrounding the lower isodose line. Lower isodose line may lead to larger dose discrepancy, while make steeper dose fall-off gradient. This phenomenon was compromised when 3-dimensional space distribution was considered.
This result may provide a prospective reference for target dose degradation due to motion during lung SBRT treatment.
本研究旨在探讨肺癌立体定向体部放疗（SBRT）期间分次内变化引起的靶区剂量差异。
基于平均计算机断层扫描（AVG CT）设计调强放射治疗（IMRT）计划，在体模和患者病例中均利用65%和85%处方等剂量线周围的计划靶区（PTV）。通过将标称计划等中心沿六个方向从0.5毫米移动到4.5毫米，步长为1毫米来模拟变化，以生成一系列扰动计划。将初始计划与扰动计划之间的剂量差异计算为初始计划的百分比。采用包括内部靶区（ITV）和大体肿瘤体积（GTV）的剂量指数作为终点样本。在三维空间分布下计算平均剂量差异。
我们发现，运动可导致肺癌SBRT中靶区和ITV的严重剂量降级，尤其是在PTV围绕较低等剂量线的SBRT期间。较低的等剂量线可能导致更大的剂量差异，同时使剂量下降梯度更陡。考虑三维空间分布时，这种现象得到了缓解。
该结果可为肺癌SBRT治疗期间因运动导致的靶区剂量降级提供前瞻性参考。
