Actual status of neutron irradiation in medical care

The application of fast neutron for the medical care has produced promising results because of its radiobiological effectiveness. Since 1975, we have designed the remotely controlled after-loading system, using 252Cf neutron sources, and have developed it for the therapy of malignant tumors. The safety of this system, especially the radiation leakage when the system is either working or not, has been surveyed by using Rem-counter and GM tubes. The results showed that the amount of radiation leakage was small enough to be neglected on the level of the radiation protection, so that operators do not mind to be exposed to the neutron radiation. Physical dosimetry of 252Cf neutron sources, which is required for the clinical application were measured with a pair of ionization chamber, so as to determine neutron and gamma ray components of the absorbed dose for the radiation therapy. On the other hands, the method how to protect against photo-neutron produced from clinical linear accelerator has been investigated. We have established one of the most efficient method to prevent the radiation, that is, two plastic doors were built in the maze. (author)