Cherenkov light is emitted in response to therapeutic x-ray beam delivery for the treatment of breast cancer, and serves as a passive, non-contact approach for measuring optical signal that is intrinsically linear with dose. However, the intensity of emitted light is attenuated due to absorbers in the tissue (blood, pigment, radiodensity, etc.). If correction for this attenuation were possible, then absolute dose imaging would be feasible. In this study, the planning CT scan was spatially sampled over the area emitting Cherenkov, and the attenuation of the signal was corrected for, using CT radiodensity. There was a linear correlation between presence of fibroglandular (high HU) versus adipose (low HU) and the emitted Cherenkov light. This relationship was used to generate scale factors to normalize out existing tissue variability in images recorded during fractionated radiotherapy, which reduced patient-to-patient variability to under 10%.
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