Purpose: In this study, a unique color Cherenkov camera was used to quantify the relationship between melanin concentration and emission intensity. Our hypothesis is that a correction factor could improve linear correlation between Cherenkov emission intensity and dose, negating effects of varying melanin concentration. This was tested in tissue phantoms with the goal of applying the technique to human imaging.
Methods: A color Cherenkov camera that captures red, green, and blue (RGB) wavelength channels separately was used in this study. Acquisition was time-gated to the LINAC, capturing Cherenkov emission only during radiation pulses, thereby removing background ambient light. To simulate tissue, synthetic epidermal layers 100 μm (+/- 5 μm) thick were fabricated, with varying biological concentrations of melanin (0.0018, 0.0038, 0.0076, 0.0114, 0.0189, 0.0273, 0.0452 and 0.0719 mg/ml). The epidermal layers were placed on top of thick bulk tissue phantoms made of silicone with flesh-colored pigment. Average optical properties (absorption coefficient, μa, and reduced scattering coefficient, μs’) of the phantoms were determined to confirm tissue-like optical behavior for a range of human skin colors. During LINAC irradiation of the phantoms, images were captured for each color channel, and post-processing extracted average RGB Cherenkov intensities vs simulated skin melanin concentration.
Results: The tissue attenuation values from melanin were compared against organic tissue optical properties of skin, particularly the calibrated reflectance average, and validated for use in this study. The color Cherenkov image analysis showed monotonically decreasing signal intensity with increasing melanin concentration, indicating that calibration of the emission for this was possible.
Conclusion: This work proposed with the color Cherenkov camera was validated by use of skin/tissue phantom models. The color Cherenkov data varied linearly with the expected attenuation by melanin in the skin, and implementing a correction factor to make Cherenkov intensity match the delivered dose values should be possible.
Funding Support, Disclosures, and Conflict of Interest: The camera and analysis software is the property of Dose Optics LLC. Dr. Brian Pogue is the CEO of Dose Optics. Dr. Petr bruza is an employee. Dr. Daniel Alexander is a consultant.