Each phantom consists of a set of nesting 15-cm thick solid PMMA disks measuring 16 cm (head) and 32 cm (body) in diameter. Handles on the body and head are provided for ease in handling and maneuverability. Through-holes measuring 1.31 cm in diameter will accommodate standard CT probes. Acrylic rods are provided to plug the holes when not in use. The acrylic rods are machined to receive 1 mm diameter TLD rods. A pediatric version in three parts is available.