Li J S, Boyer A L, Ma C M
Department of Radiation Oncology, Stanford University School of Medicine, California 94305-5304, USA.
Med Phys. 2001 Dec;28(12):2466-74. doi: 10.1118/1.1413519.
A water beam imaging system (WBIS) has been developed and used to verify dose distributions for intensity modulated radiotherapy using dynamic multileaf collimator. This system consisted of a water container, a scintillator screen, a charge-coupled device camera, and a portable personal computer. The scintillation image was captured by the camera. The pixel value in this image indicated the dose value in the scintillation screen. Images of radiation fields of known spatial distributions were used to calibrate the device. The verification was performed by comparing the image acquired from the measurement with a dose distribution from the IMRT plan. Because of light scattering in the scintillator screen, the image was blurred. A correction for this was developed by recognizing that the blur function could be fitted to a multiple Gaussian. The blur function was computed using the measured image of a 10 cm x 10 cm x-ray beam and the result of the dose distribution calculated using the Monte Carlo method. Based on the blur function derived using this method, an iterative reconstruction algorithm was applied to recover the dose distribution for an IMRT plan from the measured WBIS image. The reconstructed dose distribution was compared with Monte Carlo simulation result. Reasonable agreement was obtained from the comparison. The proposed approach makes it possible to carry out a real-time comparison of the dose distribution in a transverse plane between the measurement and the reference when we do an IMRT dose verification.
一种水束成像系统（WBIS）已被开发出来，并用于验证使用动态多叶准直器的调强放射治疗的剂量分布。该系统由一个水容器、一个闪烁体屏幕、一个电荷耦合器件相机和一台便携式个人计算机组成。相机捕获闪烁图像。该图像中的像素值表示闪烁屏幕中的剂量值。已知空间分布的辐射野图像用于校准该设备。通过将测量获得的图像与调强放射治疗计划的剂量分布进行比较来进行验证。由于闪烁体屏幕中的光散射，图像会模糊。通过认识到模糊函数可以拟合为多个高斯函数，对此进行了校正。使用10厘米×10厘米X射线束的测量图像和使用蒙特卡罗方法计算的剂量分布结果来计算模糊函数。基于使用此方法得出的模糊函数，应用迭代重建算法从测量的WBIS图像中恢复调强放射治疗计划的剂量分布。将重建的剂量分布与蒙特卡罗模拟结果进行比较。比较结果取得了合理的一致性。当我们进行调强放射治疗剂量验证时，所提出的方法使得能够在测量值与参考值之间的横向平面上实时比较剂量分布。
