||With the increasing use of 3D models and CAD in the medical domain, virtual surgical planning is now frequently used. In this paper, we propose a method to provide a fast and efficient estimation of shape and dimensions of soft tissue resections. Our approach takes advantage of a simple sketch-based interface, which allows the user to paint the contour of the resection on a patient specific 3D model reconstructed from a CT scan. From the outline of the resection defined on the skin surface as a closed curve, we can identify which areas of the skin are inside or outside this shape. We then use distance transforms to identify the soft tissue voxels which are closer from the inside of this shape. Thus, we can propagate the shape of the resection inside the soft tissue layers of the volume.