A program for correlating the position of a radiation beam with the position of a target to be irradiated and contained in a structure underlying a repetitive motion comprising a plurality of successive motion cycles, wherein the program, when running on a computer or when loaded onto a computer, causes the computer to perform the following method steps: a) acquiring, from a tracking system, first external position data, second external position data and third external position data describing the position of at least one external feature of said structure, for one or more sections of at least one first motion cycle occurring during a first period of time, for one or more sections of at least one second motion cycle occurring during a second period of time, and for one or more sections of at least one third motion cycle occurring during said second period of time, respectively; b) acquiring, from a first imaging device, first target position data and second target position data describing the position of said target for at least one of said sections of said at least one first motion cycle, and for said sections of said at least one second motion cycle, respectively; c) determining, based on said first external position data and said first target position data, correlation model data describing a positional correlation of said external position and said target position; d) determining, based on said correlation model data and said second external position data, second predicted target position data describing a predicted position of said target for one or more sections of said at least one second motion cycle; e) determining, based on said second target position data and said second predicted target position data, primary verification data describing whether the position of said target for said sections of said at least one second motion cycles is different from said predicted position; f) acquiring, from a second imaging device and in case said primary verification data indicates that the position of said target is not different from the predicted position of said target, auxiliary second target position data and auxiliary third target position data describing the position of said target for one or more sections of said at least one second motion cycle, and of said at least one third motion cycle, respectively; g) determining, based on said first and/or said second external position data, said auxiliary second target position data and said third external position data, third predicted target position data describing a predicted position of said target for said sections of said at least one third motion cycle; h) determining, based on said auxiliary third target position data and said third predicted target position data, secondary verification data describing whether the position of said target for said sections of said at least one third motion cycle is different from said predicted position. a) acquiring, from a tracking system, first external position data, second external position data and third external position data describing the position of at least one external feature of said structure, for one or more sections of at least one first motion cycle occurring during a first period of time, for one or more sections of at least one second motion cycle occurring during a second period of time, and for one or more sections of at least one third motion cycle occurring during said second period of time, respectively; b) acquiring, from a first imaging device, first target position data and second target position data describing the position of said target for at least one of said sections of said at least one first motion cycle, and for said sections of said at least one second motion cycle, respectively; c) determining, based on said first external position data and said first target position data, correlation model data describing a positional correlation of said external position and said target position; d) determining, based on said correlation model data and said second external position data, second predicted target position data describing a predicted position of said target for one or more sections of said at least one second motion cycle; e) determining, based on said second target position data and said second predicted target position data, primary verification data describing whether the position of said target for said sections of said at least one second motion cycles is different from said predicted position; f) acquiring, from a second imaging device and in case said primary verification data indicates that the position of said target is not different from the predicted position of said target, auxiliary second target position data and auxiliary third target position data describing the position of said target for one or more sections of said at least one second motion cycle, and of said at least one third motion cycle, respectively; g) determining, based on said first and/or said second external position data, said auxiliary second target position data and said third external position data, third predicted target position data describing a predicted position of said target for said sections of said at least one third motion cycle; h) determining, based on said auxiliary third target position data and said third predicted target position data, secondary verification data describing whether the position of said target for said sections of said at least one third motion cycle is different from said predicted position.