Po-Thur Eve General-12: ProLoc: An image-guided localization software for target positioning

Abstract

An image‐guided localization system has been developed for daily localization of the prostate using electronic portal images, digitally reconstructedradiographs(DRR) and implanted radio‐opaque fiducial markers or anatomic landmarks. This paper describes the computer program (ProLoc) and its potentials with particular application to the daily localization of the prostate during radiation therapytreatment. Three radio‐opaque markers are implanted in the prostate before radiotherapytreatment. Reference positions of the markers are established from orthogonal DRRimages and the center of mass determined. Before treatment each day, orthogonal images are acquired using the electronic portal image devices (EPID). Projected marker positions and the center of mass are determined and align to the reference position of the center of mass. Couch position adjustment is then performed to reposition the patient to the reference position. This software has the potential to determine prostate movement over the course of routine radiotherapy using implanted markers or anatomic landmarks. It also has the potential to determine marker migration in the prostate and gives an indication of weather the prostate is increasing or decreasing in size. Localization of the prostate within the patient and proper alignment with the radiation beam are critical components of radiotherapy. Daily target of the prostate has been shown to be technically feasible. This system provides the ability to significantly reduce treatment margins for cancers confined to the prostate. ProLoc may be used to measure the marker shifts and positions on the daily portal films with an accuracy of less than 1.5mm.