A mechanism that allows the radiation beam to be held off and turned back on to better target tumor volumes during the rhythmic movement of the patient‘s lungs in respiration. Treatment technique that detects the breathing of a patient and controls switching the MV treatment beam to reduce irradiation of healthy tissue during the patient's respiratory motion. Using an infrared tracking camera and a reflective marker placed on the patient, the respiratory gating system measures the patient’s respiratory cycle and range of motion and displays them as a waveform. Once it is determined how the tumor moves in relation to the waveform, gating thresholds are set along the waveform to mark when the tumor is in the desired portion of the respiratory cycle. These thresholds determine when the automatic gating system turns the treatment beam on and off, and whether part of the patient's respiratory cycle (phase gating) or not (amplitude gating). See also RPM respiratory gating system. Controlling the treatment beam based on respiration monitored with an infrared camera.