ABSTRACT
Objective To study the impact of main source voltage fluctuation on dose rate and dose delivery accuracy of BJ-6B accelerator. Methods The accelerator was calibrated by a voltage regulator at an output voltage of 332 V. The main source voltage fluctuation was simulated by changing the output of voltage regulator within the range of 321 - 338 V. The change of dose rate was recorded. Using a water phantom, each absorption dose was measured five times and averaged along the central beam axis at the depth of 1.5 cm, 5 cm and 10 cm, respectively, with the conditions of monitor unit: 100 MU ,field: 10 cm× 10 cm and SSD = 100 cm. The impact of voltage fluctuation on dose rate and dose delivery of BJ-6B accelerator was analyzed. Results Voltage fluctuation had an significant effect on dose rate. In a certain range, dose rate and absorption dose at different depths increased as the output voltage increased. Conclusions It is essential to equip the BJ-6B accelerator with a high accurate voltage stabilizer, and the voltage stabilizer must be adjusted to its highest accuracy.
ABSTRACT
Objective To study the maintenance of BJ-6B accelerator. Methods Analyzed retrospectively the maintenance record of BJ-6B accelerator, including phenomena, causes and handle from 2002 to 2009. Results In 231 records, there were motion-controlling 64, hand-controlling-pendant 20.modulator 41, anti-peak overload 36, charging overload 5. Flatness 7, mechanical 21, digital-display 20,others lie in magnetron power, water-cooling system, light-indicator system, dose-monitor system and wedge system. Motion-controlling system is the highest among those, followed by high-voltage modulator and mechanical system. Conclusions The down time for BJ-6B accelerator is low because of its perfect technology. To keep its stability in clinic, the hospital authorities should emphasize training of engineer for improving their maintenance ability. The engineer must be familiar with the circuit diagram, check the electric wire and machine unit on time and prepare unit for maintenance. The temperature and humidity in machine house must be controlled on demand. The engineer must pay attention to machine parameters when beam is on for avoiding the spark's damage to magnetron and accelerating-tube