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arXiv physics/0607018physics.med-ph
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放射治疗中锥形束成像和传输系统的几何校准

The geometric calibration of cone-beam imaging and delivery systems in radiation therapy

Evangelos Matsinos, Wolfgang Kaissl

摘要:

我们提出了一种方法来实现放射治疗中的锥形束成像和传输系统的几何校准;我们的方法适用于其中X射线源和平板探测器,彼此面对,在被照射物体周围的圆形轨道中移动的设备。为了从数据中提取几何参数,我们使用了一个光针体模,这是容易制造的。提出了一个具有10个自由参数(空间长度和畸变角)的模型来描述被校准的单元的几何形状和机械缺陷;引入了一些额外的参数来解释剩余效应(超出我们模型的小效应)。模型参数的值通过稳健的优化方案从针体模的一次完整扫描确定。应用该方法对两组五个逆时针(ccw)和五个顺时针(cw)扫描产生了一致的和可重复的结果。在ccw和cw扫描之间已经观察到许多差异,表明在两种旋转模式下校准的设备的不同行为。在亚像素级上实现了器件几何形状的描述。

英文摘要:

We propose a method to achieve the geometric calibration of cone-beam imaging and delivery systems in radiation therapy; our approach applies to devices where an X-ray source and a flat-panel detector, facing each other, move in circular orbits around the irradiated object. In order to extract the parameters of the geometry from the data, we use a light needle phantom which is easy to manufacture. A model with ten free parameters (spatial lengths and distortion angles) has been put forth to describe the geometry and the mechanical imperfections of the units being calibrated; a few additional parameters are introduced to account for residual effects (small effects which lie beyond our model). The values of the model parameters are determined from one complete scan of the needle phantom via a robust optimisation scheme. The application of this method to two sets of five counterclockwise (ccw) and five clockwise (cw) scans yielded consistent and reproducible results. A number of differences have been observed between the ccw and cw scans, suggesting a dissimilar behaviour of the devices calibrated in the two rotation modes. The description of the geometry of the devices was achieved at the sub-pixel level.

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