How Much Target Average Positions in Thorax Region Change Daily

Purpose: Targets in the thorax regions are subject to respiratory motion and the average position maybe changed daily. This study aims to assess the degree of target average position change in respect to the bony structure using cone-beam computed tomography (CBCT). The work further validates the planning target volume (PTV) margin used in the stereotactic body radiotherapy (SBRT) of lung cancers.