Real-time tumor tracking with preprogrammed dynamic multileaf-collimator motion and adaptive dose-rate regulation
Real-time tumor tracking with preprogrammed dynamic multileaf-collimator motion and adaptive dose-rate regulation
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DOI：
10.1118/1.2965261
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发表时间：
2008-09-01
期刊：
影响因子：
3.8
通讯作者：
Yu, Cedric
中科院分区：
文献类型：
--
作者：
Yi, Byong Yong;Han-Oh, Sarah;Yu, Cedric
作者提出了一种在自由呼吸条件下利用动态多叶准直器（MLC）运动进行实时肿瘤跟踪的新方法。与以前提出的其他肿瘤跟踪方法不同，他们的新方法使用预编程的动态MLC序列与实时剂量率控制相结合。该新方案规避了基于MLC的肿瘤跟踪中必须基于实时检测到的肿瘤运动来真实的控制MLC运动的技术挑战。通过他们的新方法，肿瘤的运动，作为呼吸相位，幅度或潮气量的函数，反映在预编程的MLC序列中。治疗过程中呼吸的不规则性通过机器剂量率的实时调节来处理，这可以根据需要有效地加快或减慢辐射的输送。该方法基于以下事实：动态辐射递送中的所有参数（包括MLC运动）都受制于累积剂量，而累积剂量又可以通过改变剂量率来加速或减速。因为商业上可获得的MLC系统不允许基于患者的呼吸信号真实的修改MLC递送序列，所以先前提出的使用MLC的肿瘤跟踪技术不能在当今的临床中容易地实施。通过使用预编程的MLC序列来处理所需的运动，大大简化了实时控制的任务。通过他们的新方案，他们称之为剂量率调节跟踪（DRRT），可以使用具有动态MLC能力的现有线性加速器来实现实时肿瘤跟踪，前提是可以从外部控制射束剂量率。如果治疗机的响应时间对剂量率调制的影响可以忽略不计，则对14名患者中的13名患者进行的跟踪误差评价导致跟踪误差小于1 mm（1 sigma）。在具有可变呼吸模式和DRRT输送的移动体模上进行的胶片测量显示，97%的测量点的伽马值小于1（对于3%和2 mm标准），而非DRRT输送仅显示87%。这项研究表明，实时跟踪是可行的DRRT，即使当病人的呼吸频率是不规则的。呼吸振幅的变化和基线漂移的影响与DRRT的跟踪误差进行了讨论，有待进一步研究，建议在临床应用这项新技术的患者选择的标准。(C)2008年美国医学物理学家协会。
The authors have developed a new method for real-time tumor tracking with dynamic multileaf-collimator (MLC) motion under condition of free breathing. Unlike other previously proposed tumor-tracking methods, their new method uses a preprogrammed dynamic MLC sequence in combination with real-time dose-rate control. This new scheme circumvents the technical challenge in MLC-based tumor tracking of having to control the MLC motion in real time, based on real-time detected tumor motion. With their new method, the movement of the tumor, as a function of breathing phase, amplitude, or tidal volume, is reflected in the preprogrammed MLC sequence. The irregularity of breathing during treatment is handled by real-time regulation of the machine dose rate, which effectively speeds up or slows down the delivery of radiation as needed. This method is based on the fact that all of the parameters in dynamic radiation delivery, including MLC motion, are enslaved to the cumulative dose, which, in turn, can be accelerated or decelerated by varying the dose rate. Because commercially available MLC systems do not allow the MLC delivery sequence to be modified in real time based on the patient's breathing signal, previously proposed tumor-tracking techniques using a MLC cannot be readily implemented in the clinic today. By using a preprogrammed MLC sequence to handle the required motion, the task for real-time control is greatly simplified. With their new scheme, which they call dose-rate-regulated tracking (DRRT), it is possible to use existing linear accelerators that have dynamic MLC capability to achieve real-time tumor tracking, provided that the beam dose rate can be controlled externally. Tracking-error evaluation for 13 patients out of 14 resulted in a tracking error of less than 1 mm (1 sigma), if the effect of the response time of the treatment machine on the dose-rate modulation can be neglected. Film measurements on a moving phantom with variable breathing patterns and DRRT delivery showed that 97% of the measurement points have gamma values less than 1 (for 3% and 2-mm criteria), while non-DRRT delivery showed only 87%. This study shows that real-time tracking is feasible with DRRT even when the patient breathing frequency is irregular. Effects of the variation of breathing amplitude and of base line drift on the tracking error with DRRT are discussed; pending further study, a criterion is suggested for patient selection in the application of this new technique in the clinic. (C) 2008 American Association of Physicists in Medicine.