A method of customized breathing maneuver guidance during radiotherapy treatment by configuring to a treatment couch an augmented reality system that includes a mounting assembly, a position measurement module to measure a distance from a fixed position to a patient anatomic region during a breathing cycle, and a breath monitoring and instruction screen viewable by the patient disposed proximal to the fixed position, where the patient monitors and controls a state of their breathing cycle in real time from breath state information displayed on the instruction screen, and determining the anatomic region for monitoring to measure the distance from the fixed position, determining a patient-customized breath hold amplitude by measuring a distance between a baseline exhale position a maximum inhale position, and entering breath hold amplitude data to a computer for subsequent breath hold guidance regardless of the treatment couch model setup and patient weight variations.