Provided is a method of generating a model, the method including generating a first model representing a change in the location or the shape of the region of interest during the respiration cycle, using diagnostic images that are obtained at two points of time in the respiration cycle and that represent the region of interest; extracting shape information of one or more tissues included in the region of interest at a shape information extractor, using a 3D ultrasound image that is obtained at one point of time in the respiration cycle; determining a characteristic point of the 3D ultrasound image corresponding to a characteristic point of the first model by matching the first model with the extracted shape information; and generating a second model by updating the first model with the determined characteristic point.