A Study On The Position Detection System Of Medical Linear Accelerator Multi-leaf Collimator

Multi-Leaf Collimator,with the characteristics of high degree of fit,small transmission penumbra,and low radiation leakage,has been applied to the tumor radiotherapy equipment for several decades.With the development of Three Dimensional Conformal Radiation Therapy(3D-CRT),Intensity Modulated Radiation Therapy(IMRT),Imaging Guided Radiation Therapy(IGRT),Biologically Conformal Radiation Therapy(BCRT)and other precise radiotherapy technology,it sets higher demands for the position accuracy of MLC blade.For example,in the Intensity Modulated Radiation Therapy,it controls the Multi-Leaf Collimator to form multi-irregular sub fields,whose different shaped subfields' superposition realized conformation of the tumor target as well as the modulation of beam.Position accuracy of MLC blade has a great effect on the whole radiotherapy,which is an important link of realizing precision radiotherapy.This paper puts forward a design proposal that is based on the medical linear accelerator multi-leaf collimator position detection system of OpenCV,which applied to the self-inspection of multi-leaf collimator.Firstly,make appropriate tag with marker for the front end of the grating blade,fix the vidicon on the center of the multi-leaf collimator;secondly,use the vidicon to obtain the video images of multi-leaf collimator movement,and send them to the PC end through USB2.0;lastly,process the obtained images,getting the internal reference of the camera making use of camera calibration,correcting the images applying camera reference,and processing the grayscale and threshold,obtain the outlines of each interested point(marked points)applying the contour extraction method,calculate and obtain the barycentric coordinates of each interested point according to the obtained outlines,and also calculate and obtain the ratio of the actual displacement of blade and the number of image pixels movement through the relation of the actual displacement of the marked points and the movement of image pixels,and finally calculate the actual displacement of the marked points through this ratio and the number of image pixels movement,such a displacement is the actual displacement of the blade.During the simulation test,the author selected 38 interested points to move 2cm,4cm,7cm,11 cm position for testing making use of this method,the vidicon can accurately capture the 38 test points,the position calculation of the interested points is accurate,and the error measured within 1mm,which meets the requirements the system.