A device for implanting radioactive seeds and non-radioactive spacers in a desired configuration in an animal body for effecting radiation therapy. An elongated hollow needle is inserted in the body. A pushing element implants the row of seeds and spacers though the hollow needle towards the desired location. A tube shaped element receives the row of seeds and spacers. A lube shaped sleeve having open ends is used to insert the tube shaped element through the needle and toward the location. The pushing elements pushes the row of seeds and spacers into the desired location while still being carried in the tube shaped element.