Imaging of moving fiducial markers during radiotherapy using a fast, efficient active pixel sensor based EPID.
Imaging of moving fiducial markers during radiotherapy using a fast, efficient active pixel sensor based EPID.
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使用基于 EPID 的快速、高效有源像素传感器对放射治疗期间移动基准标记进行成像。
DOI：
10.1118/1.3651632
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发表时间：
2011
期刊：
影响因子：
3.8
通讯作者：
Osmond JP
中科院分区：
文献类型：
--
作者：
Osmond JP
目的：这项工作的目的是研究使用实验性互补金属氧化物半导体（CMOS）有源像素传感器（APS）在放射治疗过程中跟踪移动基准标记。方法：APS的有效面积为5.4 × 5.4 cm，最大全帧读出速率为20帧s-1，可选择以更高的速率读出感兴趣区域（ROI）。它与4 mm厚的ZnWO 4闪烁体耦合，该闪烁体为6 MV X射线治疗束提供8%的量子效率（QE）。将APS与标准iViewGT平板非晶硅（a-Si）电子射野成像设备（EPID）进行了比较，QE为0.34%，帧率为2.5帧/秒。为了研究两种系统对标记进行成像的能力，将四个长度为8 mm，直径为0.8、1.2、1.6和2 mm的金色圆柱体放置在运动平台上。使用APS以20帧s-1的帧速率和143 MU min-1的剂量率采集固定标记的图像，以避免饱和。EPID图像以2.5帧/秒的最大帧速率和19 MU min-1的降低剂量率采集，以提供与APS相似的每帧剂量。在剂量为0.125至2 MU时，对两种成像仪的背景信号的信噪比（SNR）和标记物信号相对于背景的对比噪声比（CNR）进行了评价。结果：发现APS的图像质量和标记物可见性更高，SNR是EPID和CNR的2.5倍，所有四种标记物的数量级都更高。为了研究成像和跟踪移动标记的能力，移动运动平台以模拟周期为6 s、振幅为20 mm和最大速度为13.2 mm s-1的呼吸循环。在最小积分时间50 ms时，应用于APS数据的跟踪算法发现所有4个标记的成功率≥92%，位置误差≤90μm。在400 ms的积分时间，最小的标记在移动时变得难以检测。即使在最大剂量率为592 MU min− 1时，由于QE较低和积分时间较长（400 ms），使用a-Si EPID检测移动标记也很困难。结论：这项工作表明，快速读出、高QE APS可能有助于在放射治疗期间跟踪移动基准标记。需要进一步研究，以调查通过移动患者解剖结构而衰减的治疗射束中的3D标记移动的跟踪。这将需要一个更大的传感器与ROI读出，以保持速度和可管理的数据速率。
Purpose:The purpose of this work was to investigate the use of an experimental complementary metal‐oxide‐semiconductor (CMOS) active pixel sensor (APS) for tracking of moving fiducial markers during radiotherapy.Methods:The APS has an active area of 5.4 × 5.4 cm and maximum full frame read‐out rate of 20 frame s−1, with the option to read out a region‐of‐interest (ROI) at an increased rate. It was coupled to a 4 mm thick ZnWO4 scintillator which provided a quantum efficiency (QE) of 8% for a 6 MV x‐ray treatment beam. The APS was compared with a standard iViewGT flat panel amorphous Silicon (a‐Si) electronic portal imaging device (EPID), with a QE of 0.34% and a frame‐rate of 2.5 frame s−1. To investigate the ability of the two systems to image markers, four gold cylinders of length 8 mm and diameter 0.8, 1.2, 1.6, and 2 mm were placed on a motion‐platform. Images of the stationary markers were acquired using the APS at a frame‐rate of 20 frame s−1, and a dose‐rate of 143 MU min−1to avoid saturation. EPID images were acquired at the maximum frame‐rate of 2.5 frame s−1, and a reduced dose‐rate of 19 MU min−1to provide a similar dose per frame to the APS. Signal‐to‐noise ratio (SNR) of the background signal and contrast‐to‐noise ratio (CNR) of the marker signal relative to the background were evaluated for both imagers at doses of 0.125 to 2 MU.Results:Image quality and marker visibility was found to be greater in the APS with SNR ∼5 times greater than in the EPID and CNR up to an order of magnitude greater for all four markers. To investigate the ability to image and track moving markers the motion‐platform was moved to simulate a breathing cycle with period 6 s, amplitude 20 mm and maximum speed 13.2 mm s−1. At the minimum integration time of 50 ms a tracking algorithm applied to the APS data found all four markers with a success rate of ≥92% and positional error ≤90μm. At an integration time of 400 ms the smallest marker became difficult to detect when moving. The detection of moving markers using the a‐Si EPID was difficult even at the maximum dose‐rate of 592 MU min−1due to the lower QE and longer integration time of 400 ms.Conclusions:This work demonstrates that a fast read‐out, high QE APS may be useful in the tracking of moving fiducial markers during radiotherapy. Further study is required to investigate the tracking of markers moving in 3D in a treatment beam attenuated by moving patient anatomy. This will require a larger sensor with ROI read‐out to maintain speed and a manageable data‐rate.
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DOI：
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发表时间：
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期刊：
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影响因子：
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DOI：
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发表时间：
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影响因子：
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影响因子：
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