The present invention is a thorax phantom that enables simulation of tumor motion within a tissue equivalent material. The system consists of a tissue equivalent epoxy phantom representing a 15 cm axial section of the human thorax that includes simplified spine and lung anatomies. Within the phantom are thru rods of similar tissue density. The rods are attached to a computer-controlled actuator that facilitates both linear and rotational motion of the rods within the phantom. A plurality of tumor targets and radiation detectors can be placed within the rods at various locations thereby enabling the simulation of respiratory and cardiac induced tumor motions within the phantom and assessment of the effects of these motions on image acquisitions, treatment planning and radiation treatment delivery.