A patient bed for a medical treatment system is equipped with a plurality of flexible photodetector pads arranged on top surface of the patient bed, where the flexible photodetector pads generate an electrical signal from ambient lighting. A monitoring circuit monitors the electrical signal generated by the plurality of flexible photodetector pads while a patient on the patient bed, where any change in the voltage level of the electrical signal from the plurality of flexible photodetector pads represents a movement of the patient.
