Abstract
Optimum conformity between treated and prescribed radiotherapy fields is likely to be achieved when the full versatility of modern therapy equipment is reflected in the field registration method. To allow for independent jaws and custom shielding, chamfer matching has been used to register selected segments of field borders independently. In a study involving 50 clinical prescription-treatment field pairs it is shown that segmented chamfer matching is superior not only to conventional unsegmented chamfer matching but also to several other methods. An example of the clinical value of segmented chamfer matching applied to electronic portal images is given.