Statistical Analysis of Operating Efficiency and Failures of a Medical Linear Accelerator for Ten Years

Ju, Sang Gyu; Huh, Seung Jae; Han, Youngyih; Seo, Jeong Min; Kim, Won Kyou; Kim, Tae Jong; Shin, Eun Hyuk; Park, Ju Young; Yeo, Inhwan J; Choi, David R; Ahn, Yong Chan; Park, Won; Lim, Do Hoon; Park, Young Hwan

Abstract

PURPOSE: To improve the management of a medical linear accelerator, the records of operational failures of a Varian CL2100C over a ten year period were retrospectively analyzed.
MATERIALS AND METHODS
The failures were classified according to the involved functional subunits, with each class rated into one of three levels depending on the operational conditions. The relationships between the failure rate and working ratio and between the failure rate and outside temperature were investigated. In addition, the average life time of the main part and the operating efficiency over the last 4 years were analyzed.
RESULTS
Among the recorded failures (total 587 failures), the most frequent failure was observed in the parts related with the collimation system, including the monitor chamber, which accounted for 20% of all failures. With regard to the operational conditions, 2nd level of failures, which temporally interrupted treatments, were the most frequent. Third level of failures, which interrupted treatment for more than several hours, were mostly caused by the accelerating subunit. The number of failures was increased with number of treatments and operating time. The average life-times of the Klystron and Thyratron became shorter as the working ratio increased, and were 42 and 83% of the expected values, respectively. The operating efficiency was maintained at 95% or higher, but this value slightly decreased. There was no significant correlation between the number of failures and the outside temperature.
CONCLUSION
The maintenance of detailed equipment problems and failures records over a long period of time can provide good knowledge of equipment function as well as the capability of predicting future failure. More rigorous equipment maintenance is required for old medical linear accelerators for the advanced avoidance of serious failure and to improve the quality of patient treatment.