A novel imaging scheme for optical cameras used in a quality assurance detector for discrete spot scanning proton beam systems

Quality assurance detectors comprising cameras and a scintillator volume are of interest for use in spot scanning proton therapy due to its dynamic delivery. In this work, we aimed to image scanned proton beams with greater flexibility than is provided by previous systems by using an innovative camera triggering solution. The main objective was to synchronize image acquisitions with proton beam deliveries. A 3D detector composed of 3 scientific complementary metal-oxide-semiconductor cameras and a volumetric liquid scintillator (20 x20x 20 cm) were used. We identified relevant signals from the synchrotron beam delivery system to trigger the cameras. These signals were processed using an open hardware microcontroller and monitored using an oscilloscope. We evaluated the camera triggering scheme by comparing the mean signal intensity and standard deviations for triggered versus non-triggered image acquisitions at 5 energies (161.6, 140.9, 124.0, 100.9, and 85.6 MeV) with 50 spots per energy. The performance of the triggering scheme was further investigated by testing the image intensity variability for 5 energies delivered at 9 different location (2 spots/location). We also measured the background signals for different exposure times (1-1000 ms) using both triggered and non-triggered schemes. The mean signal intensity difference between triggered and non-triggered schemes was 10% +/- 0.4% for low SNR (similar to 20 dB). The image intensity variability was within 2%. The background signal intensity varied by only 0.6% from the shortest exposure time (1 ms) to the longest (1 s). We demonstrated a flexible triggering scheme using an open hardware microcontroller with a camera and scintillator detector system for a spot scanning proton beam, which will enable efficient machine quality assurance and treatment plan verification measurements in the future.