For radiation within hollow organs (natural cavities) of the body an afterloading instrument, Gammamed 12i HQR, is used. This instrument makes it possible to apply the radionuclide Iridium-192 internally within close vicinity of the tumor without having to pass through healthy tissue. After insertion of an appropriate applicator into the target organ, for example the oesophagus, the radiation source is automatically inserted into the applicator. After radiation, which is very short due to the dose-efficiency of Iridium 192, the radiation source is withdrawn back into the machine.