The high precision of planned radiotherapy treatments requires accurate positioning of the prostate in order to ensure that the tightly conformed dose distribution does not miss the prostate and result in either significant tumor underdosage, an increased dose to the rectum or bladder, or both. Precise delivery has been addressed using a variety of pre-treatment localization systems. The most direct localization of the prostate involves the use of ultrasound, computed tomography (CT), or radiography of permanently implanted fiducial markers.