Equipment and parameter settings

We used Philips Big Bore CT scanner, Varian Real-time Position Management System, Modus breathing platform and 8 models in different shapes and sizes (3 spherical, 4 cuboid, and a cylinder one; volume range: 0.52–33.50 cm³). CT scanning condition was at 120 kV, 300 mAs, with thickness of 3 mm, the rotation period 1.5 sec, the detector combination conditions 16 × 1.5 mm, the screw pitch 0.938, and the scanning bed forward speed of 22.5 mm/sec. The frequencies of the platforms were set at 10, 15 and 20 times/min, respectively. The motion amplitude of lung in the three-dimensional directions was simulated by the models, which was set at 3 mm in the x-axis, 12 mm in the y-axis, and 3 mm in the z-axis, respectively (9,10).

The study was approved by the Ethics Committee of Shandong Cancer Hospital Affiliated to Shandong University (Jinan, China). Signed informed consent was obtained from the patient or guardian.