Matsubayashi Fumiyasu, Matsuura Kosuke, Ito Yasushi, Yoshioka Yasuo
Radiation Oncology Department, Cancer Institute Hospital, Japanese Foundation for Cancer Research, 3-8-31 Ariake, Koto-ku, Tokyo 135-8550, Japan.
Phys Imaging Radiat Oncol. 2025 May 13;34:100780. doi: 10.1016/j.phro.2025.100780. eCollection 2025 Apr.
This study aimed to evaluate the impact of intrafractional diaphragm motion (IFDM) on dose accuracy in stereotactic body radiation therapy (SBRT) for lower thoracic vertebrae.
A retrospective analysis was conducted on 10 patients who underwent SBRT using volumetric-modulated arc therapy (SBRT-VMAT) for the lower thoracic vertebrae. For all patients, dynamic dose calculation (DDC) was performed, incorporating IFDM using arc-divided VMAT plans, respiratory waveforms, and four-dimensional computed tomography (4DCT). The DDC results were compared with doses calculated using time-averaging CT (AveCT) and individual-phase CT scans. Diaphragm motion was quantified using 4DCT, and the correlation between IFDM and dose perturbation was assessed.
The minimum gross tumor volume (GTV) dose was overestimated by 1.8 % in phase 0 % and underestimated by - 1.0 % in phase 50 %. A statistically significant correlation was observed between dose variation and the magnitude of IFDM. In the case with the greatest magnitude of diaphragm motion, a 4.3 % variation in GTV was observed compared with the DDC. By contrast, mid-ventilation CT and AveCT showed a mean dose variation of < 0.7 %.
This study incorporated IFDM into dose calculation for SBRT-VMAT. Static planning based on CT scans acquired at a specific phase may result in unexpected dose variations. Mid-ventilation CT and AveCT demonstrated utility in mitigating dose variations associated with IFDM. Considering the correlation between dose variation and diaphragm motion magnitude is crucial for developing effective dose perturbation strategies for IFDM.
本研究旨在评估分次内膈肌运动（IFDM）对下胸椎立体定向体部放射治疗（SBRT）中剂量准确性的影响。
对10例行下胸椎容积调强弧形放疗（SBRT-VMAT）的患者进行回顾性分析。对所有患者进行动态剂量计算（DDC），使用弧形分割VMAT计划、呼吸波形和四维计算机断层扫描（4DCT）纳入IFDM。将DDC结果与使用时间平均CT（AveCT）和各相位CT扫描计算的剂量进行比较。使用4DCT对膈肌运动进行量化，并评估IFDM与剂量扰动之间的相关性。
在0%相位时，最小肿瘤总体积（GTV）剂量被高估1.8%，在50%相位时被低估-1.0%。观察到剂量变化与IFDM幅度之间存在统计学显著相关性。在膈肌运动幅度最大的病例中，与DDC相比，GTV观察到4.3%的变化。相比之下，呼气末CT和AveCT显示平均剂量变化<0.7%。
本研究将IFDM纳入SBRT-VMAT的剂量计算中。基于特定相位采集的CT扫描进行的静态计划可能会导致意外的剂量变化。呼气末CT和AveCT在减轻与IFDM相关的剂量变化方面显示出实用性。考虑剂量变化与膈肌运动幅度之间的相关性对于制定有效的IFDM剂量扰动策略至关重要。
