An apparatus for supporting a patient during medical treatment has a patient bearing plate having an opening therein in which a medical treatment device can be inserted. The opening is entirely or partially closeable by two slide elements moveable independently of each other toward and away from each other. Each slide element is wrapped by a continuous belt, and each belt is attached to one of two opposite edges which limit the opening in the bearing plate. As the slide element is moved, the continuous belt remains stationary, with the slide element moving within the loop formed by the belt.