An image handling system, comprising: a data processing unit configured to receive: a reference image (IMG1 3D) of a deformable physical entity, a target image (IMG2 3D) of said physical entity, and a first region of interest (ROI1 3D) defining a first volume in the reference image (IMG1 3D), which first volume represents a reference image element, the reference image (IMG1 3D), the target image (IMG2 3D) and the first region of interest (ROI1 3D) containing a respective three-dimensional dataset; at least one data input unit (131, 132) configured to receive user commands (c1; c2); and a display unit configured to present graphic data reflecting the reference image (IMG1 3D), the target image (IMG2 3D) and the first region of interest (ROI1 3D), characterized in that the data processing unit is further configured to: define, in response to the user commands (c1; c2), a first contour (C1 2D) in a first plane through the target image (IMG2 3D), the first contour (C1 2D) being aligned with at least a portion of a first border of a target image element (IE 3D) in the target image (IMG2 3D), the target image element (IE 3D) corresponding to the reference image element in the reference image (IMG1 3D), the first border of the target image element (IE 3D) representing an outline of a specific organ; determine a second region of interest (ROI2 3D) defining a second volume in the target image (IMG2 3D), the second region of interest (ROI2 3D) being determined based on the first contour (C1 2D), the target image (IMG2 3D) and the first region of interest (ROI1 3D), and compute a vector field (VF 1→2) describing a relationship between the first region of interest (ROI1 3D) and the second region of interest (ROI2 3D), the second region of interest (ROI2 3D) being obtainable by transforming the first region of interest (ROI1 3D) via the vector field (VF 1→2). a data processing unit configured to receive: a reference image (IMG1 3D) of a deformable physical entity, a target image (IMG2 3D) of said physical entity, and a first region of interest (ROI1 3D) defining a first volume in the reference image (IMG1 3D), which first volume represents a reference image element, the reference image (IMG1 3D), the target image (IMG2 3D) and the first region of interest (ROI1 3D) containing a respective three-dimensional dataset; at least one data input unit (131, 132) configured to receive user commands (c1; c2); and a display unit configured to present graphic data reflecting the reference image (IMG1 3D), the target image (IMG2 3D) and the first region of interest (ROI1 3D), define, in response to the user commands (c1; c2), a first contour (C1 2D) in a first plane through the target image (IMG2 3D), the first contour (C1 2D) being aligned with at least a portion of a first border of a target image element (IE 3D) in the target image (IMG2 3D), the target image element (IE 3D) corresponding to the reference image element in the reference image (IMG1 3D), the first border of the target image element (IE 3D) representing an outline of a specific organ; determine a second region of interest (ROI2 3D) defining a second volume in the target image (IMG2 3D), the second region of interest (ROI2 3D) being determined based on the first contour (C1 2D), the target image (IMG2 3D) and the first region of interest (ROI1 3D), and compute a vector field (VF 1→2) describing a relationship between the first region of interest (ROI1 3D) and the second region of interest (ROI2 3D), the second region of interest (ROI2 3D) being obtainable by transforming the first region of interest (ROI1 3D) via the vector field (VF 1→2).