2317 - Single Pixel Cherenkov Imaging of Radiation Therapy Dose

Purpose/Objective(s): Cherenkov imaging is an emerging technology that captures the light emissions from tissue during radiation therapy, allowing for direct visualizing the radiation dose delivered to each patient in a real-time and non-contact manner. Given that radiation is pulsed from medical linear accelerator (LINAC) together with the weak Cherenkov emissions, time-gated high-sensitivity imaging is required for robust measurements. The intensified camera is the current choice for Cherenkov imaging, which, however, suffer from several limitations that deteriorate the dosimetric accuracy among other features. Single pixel imaging (SPI) is a low-cost computational imaging modality that maintains diverse superiorities such as high measurement sensitivity, dynamic range, flexible triggering, etc. By taking the specific advantages of SPI, Cherenkov imaging could be further enhanced with additional temporal and spectral information with significantly higher signal capture than with current camera systems. In this study, a prototype SPI system was developed and demonstrated here in Cherenkov imaging of LINAC dose delivery to a water tank.

Materials/

Methods: A new prototype SPI system that works at time-gated mode was developed. The TVAL3 strategy was adopted to reconstruct the image. Cherenkov emissions were produced by irradiation from a Linac with fixed photon energy of 6 MV. The integrated Monte Carlo-based treatment planning system (TPS) was used to generate simulation dose inside the water tank, taken as the reference result. In the first experiment, the SPI was performed for four regular square fields with a fixed dose rate of 600 monitor units (MU) per minute. In the second experiment, the proposed SPI system was intended to capture real-time video of dose being deposited in the water tank during the delivery of a customized step-and-shoot IMRT plan.

Results: In the first experiment, the gamma passing rates of resultant gamma maps are 95.3%, 94.7%, 92.3 and 89.8% for the 3x3, 5x5, 7x7, and 9x9 cm square beams, respectively. Overall, the projection percent depth dose (pPDD) of Cherenkov exhibited reasonable agreement with their counterparts from the TPS, with average errors of 0.48%, 0.42%, 0.65%, and 1.08% for the 3, 5, 7, and 9 cm square beams, respectively. In the second experiment, the similarity between the Cherenkov and TPS dose maps was evaluated in terms of gamma index with 3%/3mm criteria, relative deviation and SSIM. The resultant gamma pass rate was 85.9% for the 3%/3mm criteria with the SSIM being 0.85.

Conclusion: In conclusion, a time-gated SPI system was proposed for imaging Cherenkov emissions from a medical LINAC. Future iterations on the SPI setup could aim on improving the depth of field to accommodate wider ranges of in-focus area, and changing the off-axis optical design to on-axis type to eliminate the field asymmetry as discussed.