1. A method comprising: generating internal positional data about an internal target region in a patient at a first frequency; generating external positional data about motion of an external region of the patient's body using an external sensor at a second frequency that is greater than the first frequency; determining a correlation between one or more positions of the internal target region and one or more positions of the external region using the external positional data of the external sensor and the internal positional data of the internal target region; and predicting a future position of the internal target region based on the determined correlation.