A Feasibility Study of Proton Beam Dosimetry Using Cerenkov Radiation
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TU-IePD-TRACK 5-1 (Tuesday, 7/27/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]
Purpose: To study the relationship between Cerenkov photon emission and absorbed dose in water, soft tissue, and cortical bone for a primary proton beam. A proportionality constant between the number of Cerenkov photons and the absorbed dose is produced, which will aid in future dosimetry work.
Methods: A proportionality constant is introduced to quantify the amount of Cerenkov radiation emission per Gray of absorbed dose. MCNP 6.2 is then used to obtain said proportionality constant for a typical proton therapy spread-out Bragg peak. A correlation between proton energy and Cerenkov emission is also obtained for a water, soft tissue, and cortical bone phantom for proton energies of 10 – 150 MeV. The central axis depth dose curve for a solid water phantom was also produced and compared to the central axis Cerenkov emission profile to ascertain the feasibility of using Cerenkov output as an estimator of the Bragg peak location.
Results: The cortical bone emitted the most Cerenkov photons, followed by water and then soft tissue. The cortical bone produced the most Cerenkov photons due to its larger Sellmeier coefficients, and therefore larger refractive index. The differences between the water and soft tissue output is likely due to the larger electron density for water. The proportionality constant between Cerenkov photon emission and absorbed dose is 6.99 x 10⁸ photons/Gray. The Cerenkov output was found to be a poor predictor of the Bragg peak location.
Conclusion: Body parenchyma emits Cerenkov photons in proportion with increasing proton energy. A proportionality constant, which relates the quantity of Cerenkov photon emission to absorbed dose, was determined for a primary proton beam. A polyenergetic proton beam was used to incorporate some energy dependence into the parameter. The Cerenkov light output was found to be an inadequate predictor of the Bragg peak location.
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