When delineating anatomical structures in a medical image of a patient for radiotherapy planning, a processor (18) detects landmarks (24) in a low-resolution image (e.g., MRI or low-dose CT) and maps the detected landmarks to reference landmarks (28) in a reference contour of the anatomical structure. The mapped landmarks facilitate adjusting the reference contour to fit the anatomical structure. The adjusted reference contour data is transformed and applied to a second image using a thin-plate spline, and the adjusted high-resolution image is used for radiotherapy planning.