Purpose The difference between three-dimensional(3D)and four-dimensional(4D)dose is effected by factors such as tumor size and motion amplitude.To propose quantitative results about the effect by these factors,a phantom that can be possible for systematic analysis through independently controlling each factor is essential.The purpose of this study is to develop the 4D deformable lung phantom which has the above the performance and evaluate the phantoms characteristics.Method The phantom was designed in the structure that sponge including silicon tumor was inserted into acrylic cylinder simulating the lung cavity.To simulate precise and various size tumors,tumors were made by pouring liquid silicon to molds manufactured by 3D printer.Diaphragm motion was simulated in the range of amplitude from 1 to 8 cm with various breathing period using piston and programmable motor.To evaluate the characteristics of phantom,four-dimensional computed tomography image of phantom were acquired.Trajectories of tumor center-of-mass was evaluated,and diaphragm-tumor motion correlation curve was acquired through evaluating the correlation between diaphragm motion and tumor excursion for adjusting tumor motion amplitude.To quantitatively analyze the difference between 3D and 4D dose according to tumor size and motion amplitude,3D dose on the basis of internal target volume-based plan and 4D dose were calculated.Results The trajectories of tumor mainly were superior-inferior(SI)direction.Diaphragm-tumor motion correlation curve showed increasing tumor excursion of SI direction according to increase of diaphragm motion.The discrepancy of differences between 3D and 4D dose was found when the each factor is varied.Conclusion This phantom can control tumor size and motion amplitude independently and contribute quantitative analysis of the difference between 3D and 4D dose and has the potential applications for evaluating deformable registration accuracy and improving accuracy when treatment for which internal organ motion exists is planned.