Patent US 11,612,766

A method of calibrating a monitoring system (10,14) is described in which a calibration phantom (70) is located with its center located approximately at the isocenter of a treatment room through which a treatment apparatus (16) is arranged to direct radiation, wherein the surface of the calibration phantom (70) closest to an image capture device (72) of the monitoring system (10,14) is inclined approximately 45° relative to the camera plane of an image capture device of the monitoring system. Images of the calibration phantom (70) are then captured using the image capture device (72) and the images are processed to generate a model of the imaged surface of the calibration phantom. The generated model of the imaged surface of the calibration phantom (70) is then utilized to identify the relative location of the center of the calibration phantom (70) and the camera plane of the image capture device (72) which is then utilized to determine the relative location of the camera plane of the image capture device and the isocenter of a treatment room.