An algorithm for simultaneous image segmentation and nonrigid registration, with clinical application in image guided radiotherapy

This paper proposed a new strategy to assess cumulative actual dose by nonrigidly mapping treatment day dose distributions to the planning day space. The mappings were achieved using a novel integrated segmentation and nonrigid registration algorithm used in external beam prostate radiotherapy. By combining segmentation and registration, we can recover the treatment fraction image regions that correspond to the organs of interest by incorporating transformed planning day organs to guide and constrain the segmentation process; and conversely, accurate knowledge of important soft tissue structures will enable us achieve more precise nonrigid registration. The novel algorithm allows the clinician to set tighter planning margins around the target volume in the treatment plan. Clinical application and evaluation of dose delivery show the superiority of proposed method to the procedure currently used in clinical practice, i.e. manual segmentation followed by rigid registration.