Using a Monolithic Active Pixel Sensor for Monitoring Multileaf Collimator Positions in Intensity Modulated Radiotherapy

To enable in-vivo monitoring of Intensity Modulated Radiotherapy (IMRT) with minimal attenuation of the treatment field, an upstream camera system based on a Monolithic Active Pixel Sensor (MAPS) has been developed. This system has been used to precisely reconstruct the position of the Multileaf Collimators (MLC) that are used to shape the treatment field. The results show the position of a MLC is known with a precision of 6 μm with 10 seconds worth of data and 52 ±4 μm for a single frame.