Preliminary study of a clinical electron beam using highly pixelated CMOS Image Sensors

The characterization of high intensity charged particle beams at medical accelerators poses several challenges. In this work, we investigate the use of a highly segmented CMOS Image Sensors (CIS), an MT9T031 from Aptina, as a way to study the spatial homogeneity and the time stability of the beam. The approach relies on the possibility to define many adjacent small regions that perform the radiation flux measurement with sufficient precision (below 1%) to extract the spatial structure of the beam. The device has been exposed to a 10 MeV therapeutic electron beam at Santa Maria Hospital (Terni, Italy) to measure the electron flux at a distance of 140 cm. The whole sensor, using a non-linear calibration, has measured the value of the flux, then the segmentation approach has been applied to study the spatial structure of the beam. Concerning the variation in time, the current limitation of a rolling shutter CIS limits the capability to disentangle the time structure of the beam. However, in light of the possibility to obtain some CIS with the new global shutter architecture, having integration time of the order of a few tens of microseconds, the measurement procedure has been implemented and tested using similar to 1Hz frequency frame-rate, to study its limits. Uncertainty of the order of 0.5% has been reached for measurement of both spatial and time beam homogeneity.