Abstract: The invention relates to system and a method for adapting a radiotherapy treatment plan for treating a target structure within a target region of a patient body, where a planning unit (7) adapts the treatment plan on the basis of a set of influence parameters quantifying an influence of the radiation on the target region per unity intensity emission in accordance with an anatomical configuration of the target region. In a storage (8), a plurality of sets of influence parameters is stored, each set being associated with an image of the body region representing a particular anatomical configuration of the target region and the planning unit (7) is configured to select the set of influence parameters from the stored sets on the basis of a comparison between a captured image of the body region and at least one of the images associated with the sets of influence parameters.