Trouble analysis for reliability evaluation of irradiation system in HIMAC

In Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences (NIRS), the number of troubles in which failures, malfunctions, disorders, errors and human errors are included occurred in machines (hardware) and computers (software) of the irradiation system has increased year by year as the number of patient increases. We have started analyzing the events that have been recorded since 1999 to now so as to check reliability of the system and plan the program for maintaining the irradiation system. The occurrence history of the event roughly shows monotonous increase curve. The occurrence rate of the computer error has not varied so much since beginning. It means there are several latent bugs in the software. It should be noted that the hardware failures have been increasing. The system seems likely to come into the period of aging; particularly the event in which a cable breaks has begun to occur recently. The irradiation system is equipped with multifold safety interlock systems for protecting a patient from unwanted beam irradiations when a trouble occurs. For assurance of quality of the irradiation system, three kinds of maintenance are being performed. The maintenance program keeps the system highly reliable and there have been no serious damage on the treatments ever. (author)