Room: Track 1
Purpose: The underlying mechanism of radiotherapy-induced phosphenes has long been debated in the literature. Numerous theories, such as direct activation of retinal nerves by ionizing radiation, have been suggested, however, no direct evidence of this phenomenon has ever been captured. This study not only features first-time images of light generated in the eye of a patient undergoing radiation therapy, but provides data showing that this light resembles Cherenkov radiation.
Methods: A pair of intensified, time-gated, CMOS cameras (CDose Research, DoseOptics LLC, Lebanon, NH) were used to capture light exiting the eye of a patient undergoing stereotactic radiosurgery. Images were captured remotely and in real-time. Mechanistic ex vivo imaging of porcine eyes was used to evaluate the spectra, angular dependency, and determine depth of maximum emission of this light signal.
Results: An external calibration factor was used to convert raw pixel intensity to average photon radiance. The number of photons exiting the eye of a patient during radiotherapy was measured to be 2,500 photons/ms (during peak emission of the ON cycle of the pulsed beam delivery). On average, pixel intensity within the region of the lens decreased by 40% when camera-eye angles were varied from 0° – 90°. Light emission from animal eye samples was maximal at a depth of 10 mm depth and its spectra matched that of Cherenkov radiation (??²) in the range of 550 - 700 nm.
Conclusion: The technique described here provides a novel method for studying light created in the eye during radiation therapy. Spectral analysis of the light exiting the eye during radiotherapy shows that it resembles Cherenkov radiation. Since this light signal exceeds the human detection threshold for visual sensation by 2 orders of magnitude, it can contribute to phosphene perception during radiation treatment.
Funding Support, Disclosures, and Conflict of Interest: This work has been funded by NIH grants R01 EB023909, R44CA232879, and P30 CA023108 M.J. is an employee and B.P. is a president of DoseOpticsLLC. B.P. also received personal fees from DoseOptics, LLC, outside the submitted work. P.B. is the PI in SBIR subaward B02463 (prime award NCIR44CA199681, DoseOptics LLC).