Objective To study the changes in target volume and center shift in 4DCT image caused by the frequency and amplitude of tumor motion.Methods A small ball with a diameter of 2 cm was driven by a homemade human thorax model and respiratory platform to move sinusoidally,with the periods of 3.0,3.8,6.0 s,and the amplitudes of 1,2 cm,for simulating the tumor motion in lung,and then 4DCT scan was carried out.The gross target volume(GTV) from 10 phases of each group of 4DCT image was segmented,and the obtained GTV was fused to obtain internal gross target volume(ITV).Furthermore,ITVAIPand ITVMIPwere ...