Maintenance of a medical klystron linear accelerator and evaluation of the lifetime of the klystron

A 15 MeV Mitsubishi medical linear accelerator was installed at our center in June 1971. Clinical use and maintenance of the machine are reviewed. Special attention should be paid to the fact that only one klystron tube has been working for nine years. This tube has now recorded more than 17,000 filament hours, while the manufacturer's warranty time is 1,500 hours. Extension of the operating hours will significantly reduce the maintenance expenses of the machine. In this aspect, we intended to evaluate the lifetime of the Mitsubishi klystron used at several hospitals by means of a questionnaire. As a result, the following points are noticed: 1. It is advisable to keep in use a klystron tube which has been working normally for a quite long time. (Preventive replacement is unnecessary.) 2. A protective device should be provided to prevent the trouble which will follow the breakage in a klystron. 3. The present warranty time for the klystron may depend on the lifetime of individual products, including even some defective ones. If the occurrence of such products is minimized, the mean life of the klystron will be extended considerably and, consequently, the warranty time can also be prolonged to a great extent. (author)