Positioning and Tracking the Prostate During External Beam Radiation

The goal for prostate radiation therapy is to give a high dose of radiation to the prostate and a minimal dose to the healthy tissue around the prostate. It is well known that the prostate moves slightly within the pelvis and that its position varies a few millimeters from day to day. There are several methods used to position the body and the prostate accurately at the beginning of each radiation therapy session. One of the standard methods is to permanently implant small markers (gold spheres or cylinders) in the prostate and use x-rays in the radiation therapy treatment room to determine whether the markers are in the correct position. If the markers are in the correct position, then the assumption is that the prostate also is in the correct position. If the markers are not in the correct position on the x-ray, then the table that the patient lies on can be shifted so that the markers are in the right place. 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. The Beacon transponder is a small glass cylinder that contains a tiny electrical circuit. The glass vial is completely sealed and separates the internal components (i.e., the electrical circuit) from the rest of the body. The glass vial is approximately one-third of one inch long and one-tenth of one inch in diameter. Three Beacon transponders will be implanted in the prostate. They will be permanently implanted.