Methods, systems and computer-readable storage media relate to determining respiratory motion from motion data of a target to be treated. The methods may include processing motion data of a target to be treated obtained from at least one marker for at least one period. Each period including a plurality of time intervals. The processing including processing the motion data to determine an isocenter for each time interval along at least one of a plurality of axes of motion. The method may include determining at least one component of the motion data in at least one axis, the at least component corresponding to a subset of the motion data having a discrete value and/or a range of values and determining respiratory motion from at least one component of the motion data. Radiotherapy treatment can be improved by determining the respiratory motion and the impact of respiration of a target.
