Integrating respiratory gating into a megavoltage cone-beam CT system
Integrating respiratory gating into a megavoltage cone-beam CT system
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DOI：
10.1118/1.2207136
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发表时间：
2006-07-01
期刊：
影响因子：
3.8
通讯作者：
Amols, Howard
中科院分区：
文献类型：
--
作者：
Chang, Jenghwa;Sillanpaa, Jussi;Amols, Howard
我们先前已经描述了一种低剂量兆伏级锥形束计算机断层扫描（MV CBCT）系统，能够使用一个束脉冲产生投影图像。在这项研究中，我们报告了它与呼吸门控的整合，用于门控放疗。呼吸门控系统跟踪患者腹部剑突和脐之间的中间位置上的反射标记，并且当标记位置在预定义阈值之外时禁用辐射递送。我们调查两种策略获取门控扫描。在连续旋转门控采集中，线性加速器（LINAC）被设置为固定X射线模式，并且机架进行5分钟360度连续旋转，在此期间，门控系统打开和关闭辐射束，导致具有不均匀分布的投影角度的投影图像（例如，以70个弧，每个弧覆盖2度）。在门控旋转连续采集中，LINAC被设置为动态弧模式，当门控系统抑制射束时，该模式暂停机架旋转，导致扫描时间稍长（6-7分钟），但产生具有更均匀分布的投影角度的投影图像（例如，类似于两个连续投影角之间的0.8度）。我们已经在固定（对比细节和胸部）体模和协议肺部患者上测试了这两种数据采集方案。对于固定体模，使用图像中不可见的单独运动体模触发RPM系统。调整帧速率，使得每次扫描采集大约450个图像（13 MU），并使用Feldkamp滤波反投影算法重建三维断层摄影图像。门控旋转连续采集产生无呼吸伪影的重建。肿瘤在肺实质和正常组织中容易辨认，横膈和肺之间的边界清晰。对比度噪声比（CNR）相对于静止体模的非增强扫描不会降低。连续旋转门控采集扫描也产生具有可辨别解剖特征的断层图像;然而，观察到条纹伪影，CNR降低约4倍。总之，我们已经成功地开发了一个门控MV CBCT系统，以验证患者定位门控放疗。(C)2006年美国医学物理学家协会。
We have previously described a low-dose megavoltage cone beam computed tomography (MV CBCT) system capable of producing projection image using one beam pulse. In this study, we report on its integration with respiratory gating for gated radiotherapy. The respiratory gating system tracks a reflective marker on the patient's abdomen midway between the xiphoid and umbilicus, and disables radiation delivery when the marker position is outside predefined thresholds. We investigate two strategies for acquiring gated scans. In the continuous rotation-gated acquisition, the linear accelerator (LINAC) is set to the fixed x-ray mode and the gantry makes a 5 min, 360 degrees continuous rotation, during which the gating system turns the radiation beam on and off, resulting in projection images with an uneven distribution of projection angles (e.g., in 70 arcs each covering 2 degrees). In the gated rotation-continuous acquisition, the LINAC is set to the dynamic arc mode, which suspends the gantry rotation when the gating system inhibits the beam, leading to a slightly longer (6-7 min) scan time, but yielding projection images with more evenly distributed projection angles (e.g., similar to 0.8 degrees between two consecutive projection angles). We have tested both data acquisition schemes on stationary (a contrast detail and a thoracic) phantoms and protocol lung patients. For stationary phantoms, a separate motion phantom not visible in the images is used to trigger the RPM system. Frame rate is adjusted so that approximately 450 images (13 MU) are acquired for each scan and three-dimensional tomographic images reconstructed using a Feldkamp filtered backprojection algorithm. The gated rotation-continuous acquisition yield reconstructions free of breathing artifacts. The tumor in parenchymal lung and normal tissues are easily discernible and the boundary between the diaphragm and the lung sharply defined. Contrast-to-noise ratio (CNR) is not degraded relative to nongated scans of stationary phantoms. The continuous rotation-gated acquisition scan also yields tomographic images with discernible anatomic features; however, streak artifacts are observed and CNR is reduced by approximately a factor of 4. In conclusion, we have successfully developed a gated MV CBCT system to verify the patient positioning for gated radiotherapy. (C) 2006 American Association of Physicists in Medicine.