Experimentally Observed Cherenkov Light Generation in the Eye During Radiation Therapy- the flashes you see have been proven.

Experimentally Observed Cherenkov Light Generation in the Eye During Radiation Therapy

Irwin I. TendlerMEng^∗

Alan HartfordMD, PhD

Michael Jermyn PhD

Ethan LaRochelleBS

Xu CaoPhD

Victor Borza BS

Daniel AlexanderMS

Petr Bruza PhD

Jack Hoopes PhD, DVM

Karen Moodie DVM

Brian P. Marr MD

Benjamin B. Williams PhD

Brian W. Poge, PhD

David J. Gladstone, ScD

Lesley A. Jarvis MD, PhD

Email the author MD, PhD Lesley A. Jarvis

Published Online: October 25, 2019

Open Access|

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https://doi.org/10.1016/j.ijrobp.2019.10.031

Open access funded by the Author(s)

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Video 1

Light emission from an enucleated pig eye as it is irradiated with radiation sheets from various directions and gantry angles

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Purpose

Patients have reported sensations of seeing light flashes during radiation therapy, even with their eyes closed. These observations have been attributed to either direct excitation of retinal pigments or generation of Cherenkov light inside the eye. Both in vivo human and ex vivo animal eye imaging was used to confirm light intensity and spectra to determine its origin and overall observability.

Methods and Materials

A time-gated and intensified camera was used to capture light exiting the eye of a patient undergoing stereotactic radiosurgery in real time, thereby verifying the detectability of light through the pupil. These data were compared with follow-up mechanistic imaging of ex vivo animal eyes with thin radiation beams to evaluate emission spectra and signal intensity variation with anatomic depth. Angular dependency of light emission from the eye was also measured.

Results

Patient imaging showed that light generation in the eye during radiation therapy can be captured with a signal-to-noise ratio of 68. Irradiation of ex vivo eye samples confirmed that the spectrum matched that of Cherenkov emission and that signal intensity was largely homogeneous throughout the entire eye, from the cornea to the retina, with a slight maximum near 10 mm depth. Observation of the signal external to the eye was possible through the pupil from 0° to 90°, with a detected emission near 2500 photons per millisecond (during peak emission of the ON cycle of the pulsed delivery), which is over 2 orders of magnitude higher than the visible detection threshold.

Conclusions

By quantifying the spectra and magnitude of the signal, we now have direct experimental observations that Cherenkov light is generated in the eye during radiation therapy and can contribute to perceived light flashes. Furthermore, this technique can be used to further study and measure phosphenes in the radiation therapy clinic.

Summary

As ionizing radiation passes through the volume of the eye, light is generated within the vitreous fluid. We found that the eye acts as an integrating sphere – light created inside the eye exits through the lens. Using an intensified and time-gated camera, we captured light exiting the eye in real-time during patient and animal sample irradiation. By analyzing the spectra of this signal, we experimentally determined that it resembles Cherenkov emission. Light signal strength was largely homogeneous throughout the entire eye and the amount of light generated in the eye exceeds the visible detection threshold.

Introduction click to expand contents 

Methods and Materials click to expand contents 

Results click to expand contents 

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This work has been funded by NIH grants R01 EB023909 , R44 CA232879 , and P30 CA023108 .

Disclosures: M.J. is an employee and B.P. is a president of DoseOptics LLC. B.P. also received personal fees from DoseOptics, LLC, outside the submitted work. P.B. has a patent PCT/US19/19135 pending and is the principal investigator in SBIR subaward B02463 (prime award NCI R44CA199681, DoseOptics LLC). D.G, has patent US10201718B2 issued.