Quantum-CMOS image sensor assessment for Cherenkov imaging during radiotherapy

Cherenkov emission from human tissues during linac-delivered radiotherapy provides a detectable optical signal that shows the real-time dose delivery. The challenge of this modality is that the linac pulses producing Cherenkov light have short durations (2–4 μs) with low duty cycle (0.1%), and the signal reaches the camera with near single photon per pixel intensity. In this study, the ability to use an ultra-low noise (<1 e − /pixel) quantum-CMOS sensor (qCMOS) to detect Cherenkov light was tested, with optimization of the signal integration and readout timings, as related to the linac pulse structure. The signal-to-noise ratio (SNR) of the detected Cherenkov was found to be sufficient for good image quality with SNR values ranging from 100 up to 400, depending on the exposure time set per frame with noise performance surpassing an intensifier-coupled CMOS camera (iCMOS) beyond ∼50 ms of exposure time per frame. The detected signal also correlated very closely to a planned dose in a water tank with gamma pass rates of >94%. Additional advantages include low susceptibility to stray x-ray radiation. This recent development of ultra-low noise qCMOS technology is a unique option for Cherenkov imaging, showing the ability to image signals well above the noise without need for image intensifiers or gain amplification.