An optocoupler-based method for dosimetry in low energy X-ray beams

Abstract

Semiconductor electronic devices have been used as detector in X-ray beams for decades, and the principle of operation is based on measuring the electrical current generated while such a device is under the ionizing radiation. Some devices that can be used are: photodiode, phototransistor, bipolar junction transistor, MOSFET, among others. In this work, a method based on an optocoupler device is presented for radiation dose real-time measurement in low-energy X-ray beam, which is used in medical radiology. Such an optoelectronic device has an LED and a phototransistor inside it, in general, for signal communication between two circuits that have to be electrically decoupled. Therefore, the light emitted by the LED excites the phototransistor. To develop an innovative method for radiation detection, the output signal from the phototransistor is used to feed back the current source of the LED so that the phototransistor is kept at a constant operating point by the photonic intensity of the LED, which is shielded from the ionizing radiation beam to be detected. When the optocoupler is irradiated an additional signal on the phototransistor is superimposed on the signal originated by the LED. Then, a time-integrated error signal is digitized and stored in real-time. Each step of the error signal is proportional to the accumulated radiation dose during the device exposure. This innovative method was tested under different conditions varying both peak kilovoltage (kV) and workload (mAs) in order to compare with results from other electronic devices. The experimental results showed that the optocoupler-based method for X-ray dose measurement works and consequently may become an option for X-ray dosimetry.