Fig. 1From: Efficacy of virtual block objects in reducing the lung dose in helical tomotherapy planning for cervical oesophageal cancer: a planning studyAxial image of virtual blocks. a Five fan-shaped blocks in increments of 10 degrees between 40 and 80 degrees, which set the tracheal bifurcation as a central point. b Four semi-circular blocks in increments of 1Â cm between 5 and 8Â cm from the tracheal bifurcationBack to article page