IGRT combines traditional radiation treatment with a simultaneous CT scan to allow for greater precision and accuracy when targeting and treating tumors. IGRT is the process of frequent two and three-dimensional imaging, during a course of radiation treatment, to ensure that the treatment volume is being accurately targeted. Three-dimensional IGRT fuses a cone-beam computed tomography (CBCT) dataset with the computed tomography (CT) dataset from planning. Two-dimensional IGRT matches planar kilovoltage (kV) radiographs fluoroscopy or megavoltage (MV) images with digital reconstructed radiographs (DRRs) from the planning CT. The images are taken after the patient is set up for treatment. Once the image is acquired it automatically fuses with the planning CT (for 3D IGRT) or the DRRs obtained from the planning CT (for 2D IGRT). Upon fusion of the two images the therapist is able to visualize whether or not the treatment volume is off target from the planned target and make the necessary adjustments to ensure accurate treatment.