Four-dimensional cone beam computed tomography

Varying the gantry rotation time to maintain a similar image quality for different patient respiratory cycles may be necessary and has been implemented on a slow-rotation CBCT with the Varian Real-Time Position Management (RPM) system (Lu et al. 2007). This approach used a slower scan to collect the projection data of a longer breath cycle, which causes the angular spacing to be smaller between the projection data of the same phase between two consecutive breath cycles. Radiation exposure per projection can be reduced for a longer acquisition time to maintain the similar radiation dose to the patient.