Characterization of a CMOS sensor array for small field fluence measurement of a low energy proton beam

Small fields and sharp dose gradients typically encountered in proton irradiation for preclinical research require high spatial resolution dosimetric measurements, especially below 10 mm beam diameter. This study aims to characterize a complementary metal oxide semiconductor (CMOS) sensor for fluence measurement of small radiation fields (2 mm, 5 mm and 10 mm diameter) delivered by a 25 MeV proton beam dedicated to preclinical irradiations. The beam fluence was characterized in air with a MIMOSA28 CMOS sensor and EBT3 films and compared to Geant4 simulations. The measured flatness for the 10 mm field was found within ±2.5 % with both the CMOS sensor and EBT3 films. Lateral profiles were in agreement within a distance of 0.1 mm between the two detectors and Geant4 simulations. Also, with a fixed particle rate, the fluence measured by the CMOS sensor was constant at the plateau of the Bragg curve, regardless the field size, while EBT3 showed a 10% increased fluence for the 2 mm collimated beam. The CMOS sensor demonstrated a high spatial resolution and its fluence-response is independent of the radiation field sizes that seems promising for future developments in dosimetry of small field proton beams for precise irradiation platforms dedicated to preclinical research, as well as in nuclear research and laser accelerated particle beam characterization