A method and system for automatic location of a target treatment structure, such as a pulmonary vein ostium, from an anatomical image. The method includes calculating a most likely path of blood flow through a pulmonary vein based on a cross-sectional area minimization technique and calculating pulmonary vein geometry as a function of length. For example, a pulmonary vein ostium may be located by analyzing a change in pulmonary vein dimensional size or other anatomical factors, such as absolute size. The method may also include determining tissue thickness at the pulmonary vein ostium or other treatment size for treatment dose optimization. The method may be an algorithm performed by a processing unit of a navigation system or other component of a medical system.