During the irradiation of the intra-ocular tuomur, the patient must be capable to co-operate and to maintain to a fixed stare at a particular angle to concentrate the dose on the target. To increase the accuracy and reproducibility of the gaze and to avoid the error of dose distribution resulted from eye-motion, we developed a system to track the eye-motion in real time and to irradiate with the gating technique. Using infrared video image around the patient eye, the pupil and the Purkinje which is a reflection from the surface of cornea are detected by image processing. A set of these two points is applied on the eye-ball model and the angle of gaze is estimated. If the direction of gaze is moved to outside of permitted area by the rotary motion of eye ball or by the eyelid, the gate signal to beam-off is generated, and the irradiation is automatically turned off. In preliminary study using an artificial eye, our system detected the pupil position with the accuracy of less than 0.2 mm. In subjects, the minor fluctuation about 1.8 degree of the gaze direction was observed. This variation was almost equivalent to the motion of 0.4 mm on the eye surface. The total response time from the change of gaze to beam-off was less than 67 milliseconds. The accuracy of developed system would be enough clinically, and this will support the safety irradiation of ocular tumour and the quantitative verification of the patient gaze.4th Shinji Takahashi Memorial International Workshop on 3D-CR
