AbstractID: 7822 Title: Application of Image Registration for Post-Surgical Radiation
Therapy Treatment Planning
Image registration can match multiple imaging studies to a common frame of reference for fully optimized radiation therapy planning.
While best results are achieved when all imaging studies are obtained in the radiotherapy position this is not always possible or
practical, especially for patients treated post-surgery when pre-surgical images have been obtained for diagnostic purposes. We
present a technique to register pre-surgical diagnostic CT images (PS-CT) to those acquired during virtual simulation (VS-CT). Our
objective is to obtain a clinically useful estimate of the pre-surgical location of the resected organ (RO), via image registration, for the
purpose of target volume definition. Registration of PS-CT to VS-CT is complicated by several factors including differences in patient
positioning and internal organ motion. We have observed in a parallel study that relative organ positions differ significantly between
PS-CT and VS-CT. In some cases, however, image registration (rigid-body) based on mutual information (MI) produces a visibly
acceptable alignment of soft tissue organs in the region of the RO which allows its location to be estimated on the VS-CT. In other
cases, the MI algorithm returns a result showing good alignment of bony anatomy but very poor alignment of the organs of interest.
We have found that judicious manipulation of the CT images prior to registration to reduce the influence of the bony structures can
shift the results to good alignment of organs. We believe that this technique is a promising methodology to improve definition of the
tumor bed for treatment planning purposes.