A POLYGON MATCHING ALGORITHM AND ITS APPLICATIONS TO VERIFICATION OF RADIATION-FIELD PLACEMENT IN RADIOTHERAPY

An automated method for quantitative evaluation of geometric accuracy of radiation field placement during radiation therapy treatments has b een developed and is presented in this article. The method is based on matching polygons representing the boundaries of the prescribed and t reated radiation fields. An efficient algorithm for finding the inters ection of two arbitrary simple polygons has been developed for that pu rpose. The process of polygon matching is performed by iterative optim ization of the goodness-of-match measure derived from the area of the intersection between the two polygons to be matched. The optimization is done with respect to the translation and rotation in the plane that are applied to the polygon representing the treated held. The optimum translation and rotation define the adjustments in the position of th e treated field, relative to the patients anatomy, which are necessary in order to bring the treated field into the best possible agreement with the prescription. The radiation held matching scheme was applied to a clinical dataset consisting of prescription-treatment field pairs extracted from simulation and portal images for 40 patients. It is co ncluded that the observed accuracy and efficiency of the method make i t very suitable for applications in radiation therapy verification.