Liu Jie, Lin Teh, Fan Jiajin, Chen Lili, Price Robert, Ma C-M Charlie
Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA, USA.
J Appl Clin Med Phys. 2018 Sep;19(5):666-675. doi: 10.1002/acm2.12434. Epub 2018 Aug 13.
Two different respiratory monitoring systems (Varian's Real-Time Position Management (RPM) System and Siemens' ANZAI belt Respiratory Gating System) are compared in the context of respiratory signals and 4D CT images that are accordingly reconstructed. This study aims to evaluate the feasibility of combined use of RPM and ANZAI systems for 4DCT simulation and gated radiotherapy treatment, respectively.
The RPM infrared reflecting marker and the ANZAI belt pressure sensor were both placed on the patient's abdomen during 4DCT scans. The respiratory signal collected by the two systems was synchronized. Fifteen patients were enrolled for respiratory signal collection and analysis. The discrepancies between the RPM and ANZAI traces can be characterized by phase shift and shape distortion. To reveal the impact of the changes in respiratory signals on 4D images, two sets of 4D images based on the same patient's raw data were reconstructed using the RPM and ANZAI data for phase sorting, respectively. The volume of whole lung and the position of diaphragm apex were measured and compared for each respiratory phase.
The mean phase shift was measured as 0.2 ± 0.1 s averaged over 15 patients. The shape of the breathing trace was found to be in disagreement. For all the patients, the ANZAI trace had a steeper falloff in exhalation than RPM. The inhalation curve, however, was matched for nine patients, steeper in ANZAI for five patients and steeper in RPM for one patient. For 4D image comparison, the difference in whole-lung volume was about -4% to +4% and the difference in diaphragm position was about -5 mm to +4 mm, compared in each individual phase and averaged over seven patients.
Combined use of one system for 4D CT simulation and the other for gated treatment should be avoided as the resultant gating window would not fully match with each other due to the remarkable discrepancy in breathing traces acquired by the two different surrogate systems.
在呼吸信号以及据此重建的4D CT图像的背景下，对两种不同的呼吸监测系统（瓦里安的实时位置管理（RPM）系统和西门子的安赛腰带呼吸门控系统）进行比较。本研究旨在分别评估RPM和安赛系统联合用于4D CT模拟和门控放射治疗的可行性。
在4D CT扫描期间，将RPM红外反射标记和安赛腰带压力传感器均放置在患者腹部。对两个系统收集的呼吸信号进行同步。招募了15名患者进行呼吸信号收集和分析。RPM和安赛轨迹之间的差异可以通过相移和形状畸变来表征。为了揭示呼吸信号变化对4D图像的影响，分别使用RPM和安赛数据进行相位排序，基于同一患者的原始数据重建了两组4D图像。测量并比较每个呼吸阶段的全肺体积和膈肌顶点位置。
15名患者的平均相移测量值为0.2±0.1秒。发现呼吸轨迹的形状不一致。对于所有患者，安赛轨迹在呼气时的下降比RPM更陡峭。然而，吸入曲线在9名患者中匹配，在5名患者中安赛更陡峭，在1名患者中RPM更陡峭。对于4D图像比较，在每个单独阶段进行比较并在7名患者中取平均值，全肺体积差异约为-4%至+4%，膈肌位置差异约为-5毫米至+4毫米。
应避免将一个系统用于4D CT模拟而另一个系统用于门控治疗的联合使用，因为由于两种不同替代系统获取的呼吸轨迹存在显著差异，由此产生的门控窗口将无法完全相互匹配。
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