1. A system, comprising: at least one medical imaging device for generating patient images of a patient; and at least one computer for transforming a representation of an anatomical structure of a patient in a first imaging modality into a representation of the anatomical structure in a second, other imaging modality, the computer having memory and instructions that when executed, perform the following steps: acquire first modality image data describing a first modality medical image generated by the medical imaging device, the first modality medical image containing the representation of the anatomical structure in the first imaging modality; acquire atlas data describing a first modality atlas image describing a general structure of the anatomical structure in the first imaging modality, the atlas data containing information about the representation of the general structure in the second imaging modality; determine, used on the first modality image data and the atlas data, a first matching transformation between the first modality medical image and the first modality atlas image; determine, based on the first matching transformation and the first modality atlas image and the information about the representation of the general structure in the second imaging modality, a second modality image representation of the first modality medical image; acquire second modality image data describing a second modality medical image containing the representation of the anatomical structure in the second imaging modality; determine based on the second modality image representation and the second modality image data, a second matching transformation between the second modality image representation and the second modality medical image; define a structural change region in the second modality image representation, the structural change region including a placeholder representing a structural change of the anatomical structure; and adapt the second matching transformation to a difference between the representations of the anatomical structure in the second modality representation and the second modality medical image by modifying the placeholder.