Abstract

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Author(s):: TANG Zhiquan; JIANG Ze; PENG Xudong; LI Guangjun; Division of Radiation Physics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China

Keywords:: ; linear accelerator; dose monitoring and control; ionization chamber; dosimetry; beam steering

Abstract:: The dose monitoring and control system of Elekta linear accelerator were analyzed systematically from twofold view of machine physics and electronics engineering. The structure characteristics of ionization chamber and corresponding malfunction mechanisms were dissected and the differences between leakage and short circuit were also discussed. The discharge at sharp points result from dust between pole plates led to small hole or cracks of plate, moreover, the capability of resistant radiation and radiation aging of plates also resulted in cracks. Here, we summarized the causes of leakage, short circuit, open circuit, small hole and crack and the corresponding malfunctions, proposed and explained the concept of equivalent sensitive volume, and revealed that the essence of dose monitoring and control was to maintain the equal ionization current between paired plates. Finally, the maintain mechanism of profile uniformity and energy stabilization, and the adjustment methods for dosimetric quality control and troubleshooting were expounded.