基于闪烁体3D剂量测量系统中光场重聚焦位置的标定方法

放疗中基于闪烁体光场成像的3D剂量测量方法是，利用光场相机对射线在闪烁体沉积能量所产生的闪烁光进行拍照，给出每一个聚焦层的光分布后进行三维重建，进而得出剂量的三维分布。光场相机所获取图像的重聚焦位置影响闪烁光三维重建的准确性，作者提出利用棋盘格标定板进行重聚焦位置标定的方法。使用Lytro Illum光场相机拍摄置于已知位置的棋盘格标定板，经光场数据处理得到焦点堆栈序列，利用刃边法得到所有重聚焦像的高斯离焦参数σ，经比较后获得最小σ对应的重聚焦参数α，最终给出若干α和重聚焦位置的对应关系，最终完成重聚焦位置标定。与常用的刻度尺标定方法相比，高斯离焦参数减小2%～10%，有利于放疗3D剂量测量精度的提高。

Calibration method of light field refocusing position in 3D dose measurement system based on scintillator

3D dose distribution measurement in radiotherapy based on scintillator light field imaging was achieved by 3D reconstruction of scintillation light produced by the scintillator energy deposition. The refocusing position of the image obtained by the light field camera affected the accuracy of the scintillation light 3D reconstruction. A method of refocusing position calibration using checkerboard calibration plate was presented. The checkerboard calibration plate in a known position was captured by the Lytro Illum light field camera, and the focus stack sequence was obtained by the light field data processing. The Gaussian defocusing parameter σ of all refocusing images was obtained by the knife-edge method, and the refocusing parameter α corresponding to the minimum σ is obtained. Finally, the corresponding relationship between some α and refocusing position was given to complete the refocusing position calibration. Compared with the commonly used scale calibration method, the Gaussian defocusing parameter can be reduced by 2 % to 10 %, which is helpful to improve the measuring accuracy of the 3D dose in radiotherapy.