Abstract
This document describes an ITK-based implementation of intensity-based 2D/3D rigid image registration for patient setup assessment in external beam radiotherapy. The registration framework was designed to simultaneously register two projection images to a 3D image volume. The projection geometry was set up to simulate the x-ray imaging system that attached to a medical linear accelerator for cancer treatment. The normalized correlation was used as the similarity measure and the Powell's optimizer was used as the optimization method. Siddon-Jacobs fast ray-tracing algorithm was implemented to compute projection images from a 3D image volume.