Normally, it's so difficult to know where the position of tumor near lung is. Because of the respiration, the tumor change its position in the respiratory cycle. In order to determine exactly the position of tumor, we need to determine the position at a moment of the respiratory cycle. We put a marking object on a patient and the maximal position changes of object signifies the amplitude of respiratory cycle. By using an infrared camera, we could determine the phase in the respiratory cycle.
In the radiation delivery process, we could only open the gate of beam at the specified moment, normally, the end-exhale.
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