Development of an optical readout Micromegas for monitoring radiotherapy gamma rays

Abstract

Combining Micro-pattern gaseous detectors with optical imaging sensors, have been proven an effective method for accurate characterization of radiation beams. In response to the growing demand for large-area, real-time gamma rays dose monitoring in radiotherapy, an optical readout Micromegas detector was manufactured with a transparent indium tin oxide glass anode. Its effective area is 25 cm × 25 cm. Preliminary assessment employing X-ray sources yielded a spatial resolution of 375 $\mu$ m (at 10% modulation transfer function). Subsequently, the prototype was tested under clinical radiotherapy gamma rays. The results show that the linearity response exceeds 99.9% (R-squared value) for different doses. For a system-configured 100 mm field of view, the measured field size was 99.70 mm, and the penumbra width was determined to be 4.01 mm. These results indicate the good potential of this method for quality assurance in radiotherapy gamma rays. Additionally, the optical readout Micromegas is expected to be expanded to monitor other types of high-flux beams, such as medical pencil proton rays and neutron beams inspections by adding some conversion layers.