0 Preface
The WDV E-6 accelerator is a standing wave electron accelerator. The dosimeter system plays an important role in the accelerator. Its work directly affects the output dose and affects the patient's therapeutic effect and even life-threatening.
For this reason, the Vectra Accelerator adopts a dual-channel independent dosimeter system to ensure the stability of its work. Since the channel one and the channel two circuit are identical, the following only describes the working principle of the channel one as an example.
1. System overview
As the ray passes through the ionization chamber, the ionization chamber produces current signals (A, B, and C, D) proportional to the intensity of the ray and is sent to two separate channels of the dose circuit. When the monitored dose is equal to the preset on the console, the channels act together to terminate the bundle. When the channel fails for some reason, channel 2 is preset to be 30 units higher than the console, terminates the beam, and warns the operator that the machine has failed through the fault light and buzzer. The two-channel monitoring dose is digitally displayed on the console, and the emitted dose is consistently stored on another independent mechanical counter. The maximum number of doses is preset on the mechanical counter, so that even if both channels fail, the machine The counter is terminated after the preset dose has been reached, ensuring patient safety and thus achieving a three-level protection of the dose. The system also monitors the symmetry of the emitted rays in real time. If the symmetry exceeds the standard, the bundle will be terminated immediately. The specific system block diagram is shown in Figure 1.
2. Ionization chamber and power supply
The ionization chamber comprises two independent sealed penetrating ionization chambers, each having a set of signal electrodes (A, B in the upper chamber, C, D in the lower chamber), and signal electrodes A, B and C, D placed vertically. For stable operation of the ionization chamber, it must be provided with a stable -500V DC voltage and monitored. When the voltage is abnormal, the machine is protected and a fault indication occurs. The two ionization chambers are respectively rectified by 180VAC-500VDC. Circuit power supply. When the X-ray passes through the ionization chamber, it interacts with the gas molecules in it, and the positive ions are attracted to the reference electrode, and the electrons are attracted to the signal electrode, so the signal electrode actually becomes a constant current source, and the radiation is generated during the pulse. The charge output is proportional to the intensity.
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