The application of artificial vision to the monitoring of immobility and the position of patients in external therapy

The result of a radiation treatment is linked to the accuracy of the patient's position, his immobility during the treatment time and the repeatability of the patient's position during the various sessions. The psychological aspects which prevent the use of immobilisation constraints have lead radiotherapists to examine the use of artificial vision to perform qualimetry based on immobility and repositioning. As concerns immobility monitoring: the image of the scene, sampled according to a reference grid to reduce the size of the information, is compared in real time to a file which constitutes the reference to the initial position. This enables the detection of non stationary points which are indicative of local movements. To eliminate the artefacts, a check is performed over the eight neighbouring points of each sample, and only the points which represent a real movement are considered. As the quality of detection is linked to the computation time, observation windows are determined by the physician during the first session which enable detection to be limited to observation of the defined fields only. As concerns position monitoring: the positional differences between the position corresponding to the first session taken as a reference, and the position under observation to be monitored, result from the measurements obtained by the co-location of a vector modelling the current image with the vector modelling in the same manner the reference image limited by a window over the part of the image visualising the target volume. A successive presentation is made of the environmental specifications, the heuristics involved in the processing of images providing the elimination of acquisition chain interference, variations in the brightness of treatment rooms and natural physiological movements such as the blinking of cyclids, and the experimental results obtained on site