Study On A Design Of Laser Position System For CT-SIM

CT-SIM positioning system has become an important auxiliary facilitiy in the process of modern tumor radiation therapy. It plays an important role in the process of simulation before radiotherapy. The CT-SIM system can effectively protect normal tissue and vital organs around the tumor from being harm. Three-dimensional laser positioning system is the actuator of CT-SIM positioning system, which is used for calibrating the isocenter point. The three markers are projected out on the body surface to accomplish the task of marking the isocenter point of tumor. The three-dimensional laser positioning system realizes the isccenter point in the radiation therapy exactly correspond with the point which marked in the CT-SIM process. The CT-SIM process makes tumor radiation treatment process more simply and more precise.CT-SIM three-dimensional laser positioning system mainly consists of laser lamp body, the control computer and hand-held control equipment. The isocenter point is autogenerated by the CT-SIM software after the doctor outlining the tumor, the information of coordinated isocenter point will be transmitted to three-dimensional laser positioning system through the network. The three-dimensional laser positioning system drives the mechanism move to the position of marked isocenter. Meanwhile, the operator can input the control information of three orientations through digital control software interface or hand-held device, the laser will move to the corresponding position according to the control information which you inputted.This paper introduces the design of a new type of three-dimension laser positioning system, which contains three separated the light bodies, a dome light and two side lights, the dome light projectes a crosscut laser line and a sagittal laser line, and two side lights projecte out a coronal laser line respectively. The two side lights can realize the the maximal vertical lifting movement upto 700mm, and the dome light can achieve maximal horizontal movement to 600mm. The laser control system can control the laser line move on a large range of journey in three-dimensional coordinates to mark the isocenter point on the body surface. Through the design of mechanical part and the kinematics simulation for the device, assures the high accuracy of mechanical motion, and it offers parameters for the design of control part. In order to avoid the phenomenon of overshoot caused by stepping motor influencing the positioning accuracy, the design using a revolving encoder as position feedback element makes the whole system be a closed loop system, which solves the lost step problem in the process of stepping motor's moving. Moreover, the driving circuit design realizes step-motor division driving, which ensures the high accuracy. In software design, the lifting curve control method is used, which ensures the accuracy of the movement, and smoothly moves to the corresponding coordinates in a high speed. At the same time, in order to facilitate the operation, the design has a perfect function of manual control terminal, which can help the operator finish the common operations and not depend on the control computer, saving the treatment time.In short, through the precise design of the system structure, the accurate design of driving system and the design of control system, the system have many advantages, such as simple structure, rapidly response, accurately positioning, and convenient controlling and so on. The three-dimensional laser position system with accurate movement design and efficient control circuit design ensures the calibration precision of the isocenter to 0.1mm, which ensures accuracy requirement of the tumor's location effectively, and guarantees the positioning precision. The precise positioning accuracy of CT-SIM three-dimensional laser positioning system ensures the accuracy of the whole radiotherapy process, lowers normal tissues'dose, and improves the quality of patient's life.