Real-time, upstream, radiotherapy verification using a Monolithic Active Pixel Sensor System

Abstract Intensity modulated radiotherapy is a widely used technique for accurately targeting cancerous tumours in difficult locations. As treatments are becoming more complex, new methods need to be developed to monitor them. Monolithic active pixel sensors are a viable candidate for providing upstream beam monitoring during treatment. A MAPS based system can be made thin enough to have less than 1% attenuation. We have already demonstrated leaf position resolutions below 130µm at the iso-centre for 5mm wide leaves sampled 34 times per second. We have shown that the signal due to therapeutic photons can be determined and thus the dose in patient. Furthermore, the sensor works well inside an MR-linac, allowing leaf position verification even in that challenging environment.