Purpose: Recent work in our laboratory demonstrated that three-dimensional scintillator detectors comprising optical cameras and a large scintillator volume are capable of capturing real-time images of dynamic pencil-beam deliveries. In this work, we developed a new image acquisition method that allows for imaging of all of the pencil beams in a treatment plan that typically could be missed by cameras due to their dead times.
Methods: A three-dimensional detector system composed of three scientific complementary metal-oxide-semiconductor cameras and a volumetric liquid scintillator (20Ã—20Ã—20 cmÂ³) was used. The image acquisition method consisted of matching the camera acquisition intervals with the individual periods of the proton pencil beams. Multiple beam-monitoring signals generated by the synchrotron were identified, and relevant signals were selected to trigger the cameras. The camera acquisition method was validated by comparing mean light intensities captured at five discrete beam energies (from 85.6 to 161.6 MeV) with those obtained using non-triggered acquisition. The precision in capturing light intensities as a function of beam locations was also assessed.
Results: We determined that non-synchronized image acquisitions resulted in a mean light intensity loss of 10.0% Â± 0.4% compared with that in synchronized acquisitions. However, the estimated light loss corresponding to the dead time (100 Î¼s) between consecutive camera frames was only 1%. We found that the additional light loss was a function of the image signal-to-noise ratio. For example, a low ratio (~20 dB) for a single pencil beam (10-40 mGy) produced light loss of about 12% for non-triggered acquisition relative to that for triggered acquisition. The precision in recording light intensities as a function of beam locations was less than 2%.
Conclusion: Our findings demonstrated the need to develop a robust image acquisition method synchronized with proton beam delivery to accurately perform beam dosimetry using our three-dimensional detector system.