The development of a real-time respiratory motion compensation and simulated gated-radiotherapy system

Abstract

The apparatus which can trace and compensate the organ motion and abdominal motion induced by respiration on real-time is developed for respiratory-gated radiotherapy. The apparatus consists of two sections. One is the compensation planning part and the other is motion compensation treatment part. This is composed of an image grabber, a camera to detect the abdominal surface motion, a pair of tungsten gate to open and close the radiation, servo motors and controllers to control the gates. That is composed of two image grabbers, a camera and the fluoroscopy system. Software interfaced to a camera and fluoroscopy tracks the internal anatomy target and abdominal surface induced by respiration simultaneously, without any additional physical marker. The system was evaluated based on the optical density and penumbra area according to the respiratory period, motion distance and duty cycle. The optical density was lessened linearly according to the duty cycle. Density relative errors were less than 0.02[level/level]. Also the penumbra was lessened according to both the motion distance and the duty cycle. The penumbra was measured by the distance between the 10% and 90% levels. The outstanding point of developed system is robust about the environment changing like unstable illumination or pattern changing. We have acquired 10 data of abdominal surface motion induced by respiration and organ motion using the developed system. The features of respiratory motion data are that respiration pattern is not stable both period and magnitude even under the regular condition and the expiration status is longer than inspiration it. Therefore, magnitude gating method was selected primary gating method and phase gating method was used by assistant method. Also, it was desirable to open the gate respect to expiration than inspiration.