Technical aspects of real time positron emission tracking for gated radiotherapy
Technical aspects of real time positron emission tracking for gated radiotherapy
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DOI：
10.1118/1.4939664
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发表时间：
2016-02-01
期刊：
影响因子：
3.8
通讯作者：
Xu, Tong
中科院分区：
文献类型：
--
作者：
Chamberland, Marc;McEwen, Malcolm R.;Xu, Tong
目的：呼吸运动可能导致放射治疗输送中的治疗错误。呼吸门控可以帮助更好地使射束递送符合目标体积。我们提出了一个真实的时间正电子发射跟踪系统的技术方面的研究，用于门控radiotherapy.Methods：该跟踪系统，称为PeTrack，使用植入的正电子发射标记和位置敏感的伽马射线探测器来跟踪呼吸运动在真实的时间。PeTrack使用期望最大化算法来跟踪基准标记的运动。归一化最小均方自适应滤波器提前短时间预测标记的位置，以考虑系统响应延迟。在模拟门控放射治疗的条件下测量了原型PeTrack系统的精度和数据收集效率。胸部体模的肺插入物在下上级方向上平移，具有规则的正弦运动和模拟的患者呼吸运动（最大运动幅度10 mm，周期4 s）。系统每隔0.2 s跟踪嵌入肺插入物中的22 Na基准标记（0.34 MBq）的运动。提前0.2s预测了WAS标记的位置。对于正弦运动，将用于对运动建模的方程拟合到数据。跟踪的精度估计为残差的标准差。还开发了软件，用于与直线加速器和肘节束传输进行通信。在涉及直线加速器的单独实验中，使用3 x 3 cm光子束和6和10 MV加速电位向体模输送500个监测单位的辐射。将辐射变色胶片插入体模中以测量空间剂量分布。在该实验中，运动周期被设置为60秒以考虑射束开启延迟。当标记移动到5 mm门控窗口之外时，光束被关闭。结果：对于正弦运动目标，IS方向上的跟踪精度为0.53 mm，平均计数率为250 cps。当标记根据患者不规则呼吸运动移动时，平均预测误差为1.1 0 6 mm。在辐射变色胶片测量期间的所有射束输送中，平均预测误差为0.8 ± 0.5 mm。最大误差为2.5 mm，第95百分位误差为1.5 mm。在门控和非门控输送之间观察到剂量分布的明显改善。门控给药的剂量分布的半峰全宽与静态参考剂量分布相差3 mm或更小。监测的光束开/关时间显示同步的位置内的标记的latency of the system.Conclusions：PeTrack可以跟踪运动的内部基准正电子发射标记亚毫米精度。该系统可用于基于移动基准标记的位置来门控直线加速器射束的递送。这突出了该系统用于放射性门控放射治疗的潜力。(C)2016年美国医学物理学家协会。
Purpose: Respiratory motion can lead to treatment errors in the delivery of radiotherapy treatments. Respiratory gating can assist in better conforming the beam delivery to the target volume. We present a study of the technical aspects of a real time positron emission tracking system for potential use in gated radiotherapy.Methods: The tracking system, called PeTrack, uses implanted positron emission markers and position sensitive gamma ray detectors to track breathing motion in real time. PeTrack uses an expectation maximization algorithm to track the motion of fiducial markers. A normalized least mean squares adaptive filter predicts the location of the markers a short time ahead to account for system response latency. The precision and data collection efficiency of a prototype PeTrack system were measured under conditions simulating gated radiotherapy. The lung insert of a thorax phantom was translated in the inferior superior direction with regular sinusoidal motion and simulated patient breathing motion (maximum amplitude of motion 10 mm, period 4 s). The system tracked the motion of a 22Na fiducial marker (0.34 MBq) embedded in the lung insert every 0.2 s. The position of the was marker was predicted 0.2 s ahead. For sinusoidal motion, the equation used to model the motion was fitted to the data. The precision of the tracking was estimated as the standard deviation of the residuals. Software was also developed to communicate with a Linac and toggle beam delivery. In a separate experiment involving a Linac, 500 monitor units of radiation were delivered to the phantom with a 3 x 3 cm photon beam and with 6 and 10 MV accelerating potential. Radiochromic films were inserted in the phantom to measure spatial dose distribution. In this experiment, the period of motion was set to 60 s to account for beam turn-on latency. The beam was turned off when the marker moved outside of a 5-mm gating window.Results: The precision of the tracking in the IS direction was 0.53 mm for a sinusoidally moving target, with an average count rate 250 cps. The average prediction error was 1.1 0 6 mm when the marker moved according to irregular patient breathing motion. Across all beam deliveries during the radiochromic film measurements, the average prediction error was 0.8 0.5 mm The maximum error was 2.5 mm and the 95th percentile error was 1.5 mm Clear improvement of the dose distribution was observed between gated and nongated deliveries. The full-width at halfmaximum of the dose profiles of gated deliveries differed by 3 mm or less than the static reference dose distribution. Monitoring of the beam on/off times showed synchronization with the location of the marker within the latency of the system.Conclusions: PeTrack can track the motion of internal fiducial positron emission markers with submillimeter precision. The system can be used to gate the delivery of a Linac beam based on the position of a moving fiducial marker. This highlights the potential of the system for use in respiratory-gated radiotherapy. (C) 2016 American Association of Physicists in Medicine.