Image-Guided Radiotherapy (IGRT) techniques: Panel A illustrates 5 implanted gold fiducial markers that serve as a three-dimensional X-Ray targeting reference, to allow fine tuning of the beam aiming before each daily radiation treatment. Panel B illustrates surgical clips in a post-prostatectomy patient that may be used in the same way as implanted gold fiducial markers (which is why we don't typically need to implant gold fiducial markers in post-prostatectomy patients). Panel C illustrates a cone-beam CT image, which is the IGRT method chosen for this post-prostatectomy patient, who has no visible surgical clips or fiducial markers. When cone beam CT is used for IGRT, the visualized organs seen at each daily CT session are matched with their planning CT counterparts, illustrated by colored outlines of the prostate bed (red), bladder (violet) and rectum (tan) in this figure.