In this study the Beacon® transponder will be used in place of the standard gold marker. During the radiation therapy visits, the patient position in the treatment room will be corrected using the Beacon transponder with an investigational system, called the Calypso® 4D Localization System. The Calypso system consists of a flat panel, placed over the pelvis and connected to a computer, which monitors the position of the Beacon transponders within the prostate. During five radiation therapy appointments and one extra visit, the position of the markers in the prostate will be confirmed with x-rays.