ABSTRACT
In respiratory gating, the tumor position is measured during the respiration cycle. Assuming the tumor position reliably returns to a xed position at a certain respiration state, the radiation beam can be “gated” to this respiration state such that the beam is on only when the tumor is at the xed reference position. Because of the diculty in directly measuring the tumor position in real time, surrogate signals such as spirometry, optical tracking of the patient surface, or external markers are used. A signicant portion of the quality control process is designed to verify and update the strength of the relationship between the surrogate and the tumor position.
