A New Method Of Isocenter Measurement And Error Analysis

The medical linear-accelerator is designed according to the principle of the same center.It’s treatment bed and the arm can rotate around the same point,and the radiation axis should pass from the smallest sphere centered on this point,which called the isocenter.Nowdays,cancer is one of the most serious problems in our society,and the medical linear-accelerator had been the most populer equipment in radiotherapy.As the quality assurance and the quality control of the medical linear-accelerator,it’s very important to judge the accuracy of the isocenter.There are many ways to measure the isocenter,but they are nearly similar,mostly using the laser light or ranging lights artificially.These methods have large random errors.The after-sales service of the linear-accelerator,which is professional,always toke too much time and cost a lot.To solve these problems,I designed a new method to measure the isocenter,which is easy and automatic.The new method is base on Oncology Positioning System(OPS)which is installed in some hospital in recent years.The new method is also based on the infrared direction technology.We use the least square method to fitting the movements of the equipment,and then calculate the accurate three-dimensional coordinate of the isocenter under the CT coordinate system.In this paper,the uncertainty of the distance measurement and the uncertainty of the angle measurement are analyzed theoretically.The isocenter coordinates obtained by the new method are compared with the results of the old method.According to the experiment,We can draw a conclusion that the error is less than one millimeter with our new method.