A novel approach for the registration of 2D portal and 3D CT images for treatment setup verification in radiotherapy

Abstract

In this paper we present a framework to simultaneously segment portal images and register them to 3D treatment planning CT data sets for the purpose of radiotherapy setup verification. Due to the low resolution and low contrast of the portal image, taken with a high energy treatment photon beam, registration to the 3D CT data is a difficult problem. However, if some structure can be segmented in the portal image, it can be used to help registration, and if there is an estimate of the registration parameters, it can help improve the segmention of the portal image. The minimax entropy algorithm proposed in this paper evaluates appropriate entropies in order to segment the portal image and to find the registration parameters iteratively. The proposed algorithm can be used, in general, for registering a high resolution image to a low resolution image. Finally, we show the proposed algorithm’s relation to the mutual information [19] metric proposed in the literature for multi-modality image registration.KeywordsMutual InformationTransformation ParameterPortal ImageJoint Density FunctionReal Portal ImageThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.