Characterization of Cherenkov Emission and Field Size Verification Using Optical and Epid Imaging
Abstract
Purpose
To characterize surface Cherenkov emission as a function of photon beam energy and dose rate, and to investigate the feasibility of Cherenkov imaging for radiation field size verification using EPID measurements as a reference for patient treatments.
Methods
Cherenkov images were acquired on RW3 slab phantoms with an ASA slab on top using a high-sensitivity CMOS camera during irradiation with 6 MV, 6 FFF, 10 MV, and 10 FFF photon beams. Energy dependence was assessed at a fixed dose rate of 400 MU/min, and dose-rate linearity was evaluated from 100 to 2400 MU/min. Integrated Cherenkov intensity was extracted from a fixed surface ROI after background subtraction. Square (3×3–7×7 cm²) and rectangular fields were delivered for field size verification. Cherenkov images were captured simultaneously with EPID images, corrected for perspective distortion, while EPID images were reconstructed at the entrance surface plane. Field sizes were then computed from both modalities.
Results
At constant dose rate, normalized Cherenkov intensity decreased with increasing beam energy and for FFF beams, with reductions of 7.1% (6 FFF), 14.9% (10 MV), and 17.4% (10 FFF) relative to 6 MV. Cherenkov intensity exhibited excellent linearity with dose rate for all beams (R² = 0.9996–0.9998). After geometric correction, Cherenkov measurements consistently overestimated the expected field size by about 0.05–0.18 cm. EPID measurements matched the expected values, with deviations within 0.02–0.05 cm. Cherenkov therefore shows a small but systematic scaling offset, while EPID remains geometrically accurate.
Conclusion
Cherenkov imaging demonstrated linear dose‑rate response and consistent field size estimation across photon beams, with only a small geometric offset. When referenced to EPID, Cherenkov images provided reliable entrance‑surface field verification. These results indicate that Cherenkov imaging is feasible for in vivo surface field verification and motion‑sensitive localization (e.g., respiratory motion), serving as a complementary tool to EPID.