Video 2. Pre-treatment 4D CBCT imaging for daily registration of a lung tumor under abdominal compression.

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The patient couch was translated using the calculated registration errors. The video shows that the tumor at the end-expiration is observed at the superiormost position in the gating window ITV (in sky blue color) after the couch adjustment, where the gating window ITV was defined as an ITV considering only respiratory phases within the gating window. In other words, 4D CBCT imaging allows us to accurately and precisely position the tumor at the end-expiration, which is very important in our workflow. Respiratory hysteresis was also observed in the video, presumably leading to an unsymmetrical gating window as typically shown in Figures 3a, 3b.

CBCT: cone-beam computed tomography; ITV: internal target volume