Development of the Image Registration Program for Portal and DRR Images in Radiation Therapy

In this article, the authors propose an image registration program of portal images and digitally reconstructed radiography (DRR) images used as simulation images for external beam radiation therapy planning. First, the center of the radiation field in a portal image taken using a computed radiograhy cassette is matched to the center of the portal image. Then scale points projected on a DRR image and the portal image are deleted, and the portal image with the radiation field is extracted. Registration of the DRR and portal images is performed using mutual information as the registration criterion. It was found that the absolute displacement misregistrations in two directions (x, y) were 1.2±0.7 mm and 0.5 ±0.3 mm, respectively, and rotation disagreement about the z axis 0.3±0.3°. It was concluded the proposed method was applicable to image registration of portal and DRR images in radiation therapy