1. A method comprising: calculating deformation fields based on a plurality of x-ray images of a target, the x-ray images generated at different time points, the deformation fields representing a movement of the target at the different time points, each of the deformation fields having a plurality of vectors representative of changes in the target between two of the x-ray images; selecting a first deformation field associated with a first time point, and a second deformation field associated with a second time point, the first and second deformation fields selected from the calculated deformation fields; and determining an interpolation parameter associated with a third time point using a processor, the interpolation parameter being configured for calculating an interpolated deformation field having a plurality of vectors associated with the third time point, the interpolation parameter determined using the selected first and second deformation fields; and storing the interpolation parameter.