Wu Huanmei, Zhao Qingya, Berbeco Ross I, Nishioka Seiko, Shirato Hiroki, Jiang Steve B
Purdue School of Engineering and Technology, Indiana University School of Informatics, IUPUI, Indianapolis, IN, USA.
Phys Med Biol. 2008 Dec 21;53(24):7137-50. doi: 10.1088/0031-9155/53/24/009. Epub 2008 Nov 26.
Precise localization of mobile tumor positions in real time is critical to the success of gated radiotherapy. Tumor positions are usually derived from either internal or external surrogates. Fluoroscopic gating based on internal surrogates, such as implanted fiducial markers, is accurate however requiring a large amount of imaging dose. Gating based on external surrogates, such as patient abdominal surface motion, is non-invasive however less accurate due to the uncertainty in the correlation between tumor location and external surrogates. To address these complications, we propose to investigate an approach based on hybrid gating with dynamic internal/external correlation updates. In this approach, the external signal is acquired at high frequency (such as 30 Hz) while the internal signal is sparsely acquired (such as 0.5 Hz or less). The internal signal is used to validate and update the internal/external correlation during treatment. Tumor positions are derived from the external signal based on the newly updated correlation. Two dynamic correlation updating algorithms are introduced. One is based on the motion amplitude and the other is based on the motion phase. Nine patients with synchronized internal/external motion signals are simulated retrospectively to evaluate the effectiveness of hybrid gating. The influences of different clinical conditions on hybrid gating, such as the size of gating windows, the optimal timing for internal signal acquisition and the acquisition frequency are investigated. The results demonstrate that dynamically updating the internal/external correlation in or around the gating window will reduce false positive with relatively diminished treatment efficiency. This improvement will benefit patients with mobile tumors, especially greater for early stage lung cancers, for which the tumors are less attached or freely floating in the lung.
实时精确确定移动肿瘤的位置对于门控放射治疗的成功至关重要。肿瘤位置通常从内部或外部替代物中获取。基于内部替代物（如植入的基准标记）的荧光透视门控是准确的，然而需要大量的成像剂量。基于外部替代物（如患者腹部表面运动）的门控是非侵入性的，然而由于肿瘤位置与外部替代物之间相关性的不确定性，其准确性较低。为了解决这些问题，我们建议研究一种基于混合门控并进行动态内部/外部相关性更新的方法。在这种方法中，高频（如30Hz）采集外部信号，而稀疏采集内部信号（如0.5Hz或更低）。内部信号用于在治疗期间验证和更新内部/外部相关性。基于新更新的相关性从外部信号中得出肿瘤位置。介绍了两种动态相关性更新算法。一种基于运动幅度，另一种基于运动相位。对9例具有同步内部/外部运动信号的患者进行回顾性模拟，以评估混合门控的有效性。研究了不同临床条件（如门控窗口大小、内部信号采集的最佳时机和采集频率）对混合门控的影响。结果表明，在门控窗口内或其周围动态更新内部/外部相关性将减少假阳性，同时治疗效率相对降低。这种改进将使患有移动肿瘤的患者受益，尤其是对于早期肺癌患者，这类肿瘤在肺内附着较少或自由漂浮。
