An assembly for heat treating an area of biological tissue, including an energy generating device for supplying energy to a focal point in said area, a device for measuring the spatial temperature distribution in said area, and a control unit for controlling the movement of the focal point along a predetermined path to give a spatial temperature distribution consistent with a pre-sent distribution, characterized in that, as the focal point moves along the path, the control unit controls the distribution of the energy provided by the generating device depending on the measured temperature distribution and the pre-set distribution, in accordance with a control law including a proportional-integral-derivative term.
