At least one laser line is projected onto a surface of a patient located on a patient table, and is detected. An evaluation and control apparatus determines initial coordinate points along a laser line projected onto the surface of the patient during an initial radiation procedure based on measurement values associated with the at least one laser line detected through an initial real-time triangulation process. The initial coordinate points are compared with target coordinate points for patient positioning. Whether or not an impermissible deviation exists between the initial coordinate points and the target coordinate points is determined, and a corrective action is executed based on the determination that an impermissible deviation exists. Determining updated coordinate points occurs while corrective action is being executed, and a warning signal is emitted based on the updated coordinate points.