School of Mathematical and Physics Sciences, University of Newcastle, Newcastle, New South Wales 2308, Australia.
Med Phys. 2013 Jul;40(7):071703. doi: 10.1118/1.4807640.
To develop a method for removing the support arm backscatter from images acquired using current Varian electronic portal imaging devices (EPIDs).
The effect of arm backscatter on EPID images was modeled using a kernel convolution method. The parameters of the model were optimized by comparing on-arm images to off-arm images. The model was used to develop a method to remove the effect of backscatter from measured EPID images. The performance of the backscatter removal method was tested by comparing backscatter corrected on-arm images to measured off-arm images for 17 rectangular fields of different sizes and locations on the imager. The method was also tested using on- and off-arm images from 42 intensity modulated radiotherapy (IMRT) fields.
Images generated by the backscatter removal method gave consistently better agreement with off-arm images than images without backscatter correction. For the 17 rectangular fields studied, the root mean square difference of in-plane profiles compared to off-arm profiles was reduced from 1.19% (standard deviation 0.59%) on average without backscatter removal to 0.38% (standard deviation 0.18%) when using the backscatter removal method. When comparing to the off-arm images from the 42 IMRT fields, the mean γ and percentage of pixels with γ < 1 were improved by the backscatter removal method in all but one of the images studied. The mean γ value (1%, 1 mm) for the IMRT fields studied was reduced from 0.80 to 0.57 by using the backscatter removal method, while the mean γ pass rate was increased from 72.2% to 84.6%.
A backscatter removal method has been developed to estimate the image acquired by the EPID without any arm backscatter from an image acquired in the presence of arm backscatter. The method has been shown to produce consistently reliable results for a wide range of field sizes and jaw configurations.
开发一种从当前瓦里安电子射野影像装置（EPID）采集的图像中去除支撑臂背散射的方法。
使用核卷积方法对臂背散射对 EPID 图像的影响进行建模。通过将带臂图像与无臂图像进行比较，优化模型的参数。该模型用于开发一种从测量的 EPID 图像中去除背散射影响的方法。通过将背散射校正后的带臂图像与测量的无臂图像进行比较，对背散射去除方法的性能进行了测试，比较了 17 个不同大小和位置的矩形射野在成像仪上的图像。该方法还使用来自 42 个强度调制放射治疗（IMRT）场的带臂和无臂图像进行了测试。
使用背散射去除方法生成的图像与无背散射校正的图像相比，一致性更好。对于研究的 17 个矩形射野，与无背散射去除相比，平面内轮廓的均方根差相对于无臂轮廓的平均降低了 1.19%（标准偏差为 0.59%），当使用背散射去除方法时，降低到 0.38%（标准偏差为 0.18%）。当与 42 个 IMRT 场的无臂图像进行比较时，除了一张图像外，其余所有图像的γ均值和γ<1的像素百分比都通过背散射去除方法得到了改善。在所研究的 IMRT 场中，使用背散射去除方法后，γ值（1%，1mm）的平均值从 0.80 降低到 0.57，而γ通过率从 72.2%增加到 84.6%。
开发了一种从存在臂背散射的 EPID 图像中估计无臂背散射获得的 EPID 图像的背散射去除方法。该方法已证明对于广泛的射野大小和准直器配置均能产生可靠的结果。
