Figure 1.

OARtrac system: (top left) schematic of the PSD sensors and the fiducial (marker bead); (top right) overhead schematic of the endorectal balloon with the PSD sensor connected. Note that the sensor is attached to the top side of the balloon. Bottom left: PSD sensor outside of the endorectal balloon. Bottom right: Overhead view of the PSD sensor inside of the endorectal balloon and the fiber optic cables that will connect to the CCD camera system. The sensor is attached to the top side of the balloon, which would be placed against the anterior rectal wall.