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A Monte Carlo Analysis of the Relationship Between Cherenkov Light Emission and Dose for Electrons, Protons, and X-Ray Photons

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A Glaser

A Glaser1*, R Zhang2 , D Gladstone3 , B Pogue1,2 , (1) Thayer School of Engineering, Dartmouth College, NH, (2) Department of Physics and Astronomy, Dartmouth College, Hanover, NH, (3) Dartmouth Hitchcock Medical Center, Lebanon, NH


SU-E-J-9 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: A number of recent studies have proposed that light emitted by the Cherenkov effect may be used for a number of radiation therapy dosimetry applications. Here we investigate the fundamental nature and accuracy of the technique for the first time by using a theoretical and Monte Carlo based analysis.
Methods: Using the GEANT4 architecture for medically-oriented simulations (GAMOS) and BEAMnrc for phase space file generation, the light yield, material variability, field size and energy dependence, and overall agreement between the Cherenkov light emission and dose deposition for electron, proton, and flattened, unflattened, and parallel opposed x-ray photon beams was explored.
Results: Due to the exponential attenuation of x-ray photons, Cherenkov light emission and dose deposition were identical for monoenergetic pencil beams. However, polyenergetic beams exhibited errors with depth due to beam hardening, with the error being inversely related to beam energy. For finite field sizes, the error with depth was inversely proportional to field size, and lateral errors in the umbra were greater for larger field sizes. For opposed beams, the technique was most accurate due to an averaging out of beam hardening in a single beam. The technique was found to be not suitable for measuring electron beams, except for relative dosimetry of a plane at a single depth. Due to a lack of light emission, the technique was found to be unsuitable for proton beams.
Conclusions: The results from this exploratory study suggest that optical dosimetry by the Cherenkov effect may be most applicable to near monoenergetic x-ray photon beams (e.g. Co-60), dynamic IMRT and VMAT plans, as well as narrow beams used for SRT and SRS. For electron beams, the technique would be best suited for superficial dosimetry, and for protons the technique is not applicable due to a lack of light emission.

Funding Support, Disclosures, and Conflict of Interest: NIH R01CA109558 and R21EB017559.

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