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Characterization of the Angular Scattering Distribution From Cherenkov Light Created in Phantom Materials During External Beam Therapy

E Brost

E Brost1*, Y Watanabe1 , A Green2 , (1) University of Minnesota, Minneapolis, MN, (2) University of Saint Thomas, St. Paul, MN


SU-E-108-1 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 108

Purpose: To determine an observation-angle correction factor associated with the radiance profile of Cherenkov light generated in a tissue phantom during external beam therapy in order to reduce measurement uncertainty between Cherenkov light detected and dose deposition.

Methods: GAMOS, a Geant4-based Monte Carlo framework was used to simulate the transport of Cherenkov photons created during external beam treatments. The simulations scored radiant and spectral properties of Cherenkov light in skin and optical phantoms under different irradiation conditions. A layered skin model was used to represent the skin phantom, while a solid optical phantom was simulated based upon specifications of an experimental phantom. Mie scattering and absorption coefficients were defined for all materials. For both electron and photon beams, the effects of beam angle (0-75°), energy (6-20 MeV), and field size (pencil beam-20x20 cm²) on the radiance profile of Cherenkov photons exiting the phantom were investigated. Experimental validation of results was performed on the optical phantom using a commercial CMOS camera to detect and measure light intensity at different observation angles.

Results: The simulated radiance profile of Cherenkov photons exiting the optical phantom closely follows known bidirectional reflectance distributions (BRDFs) of human skin for observation angles up to 75°. The measured radiance of Cherenkov photons exiting the optical phantom matches human skin BDRF for observation angles between 60-80°. The radiance profile created from photon beams is distinct from electron beams. The radiance profile generated by both photon and electron beams does not show a dependence on field size, energy, or angle of incidence.

Conclusion: The radiance profiles from Cherenkov photons exiting the skin surface can be used as a correction factor of Cherenkov light dosimetry in both electron and photon external beam therapies. These profiles show dependence on angle of observation, but not on radiation beam size, angle, or energy.

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