Video-coaching as biofeedback tool to improve gated treatments: Possibilities and limitations.

For respiratory gated radiotherapy the manufacturers of linear accelerators offer dedicated gating technologies. The video-based Varian RPM Gating system (Varian Medical Systems, Palo Alto/CA, USA) includes in a standard configuration a support tool for regular breathing called audiocoaching. As this approach has limitations regarding direct control of the patient's breathing due to a missing feedback, we designed an additional tool offering videocoaching. In order to evaluate the impact of this additional functionality, we measured parameters defining the image quality of 4D-CT data as well as the treatment duration which is mainly influenced by the patient's limited ability to achieve a stable breathing pattern.