Computed tomography images are usually acquired for radiotherapy planning. The DiscoveryTM RT CT simulator in our centre is able to perform four-dimensional computed tomography (4DCT) . It works together with an infrared system that detects patient breathing motion during the scan. Breathing motion signals are incorporated into the acquired CT images in favor of visualizing tumor motion in 4DCT. It assists the oncologists in customizing the radiation treatment plan for individuals.