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Dosimetric Evaluation of the Transmission and Backscatter Doses Due to Tungsten Eye Shields in High Energy Electron Fields

D Vile

D Vile1*, B Overshiner2 , P Yearling3 , C Desrosiers1 , (1) Indiana University, Indianapolis, IN, (2) Indiana University Health, Indianapolis, IN, (3) Indiana University Purdue University Indianapolis, Indianapolis, IN


SU-I-GPD-T-60 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To quantify the transmission and backscatter dose of high energy electrons incident on tungsten eye shields.

Methods: Transmission measurements were taken for 5 electron energies (range 6-20 MeV) using a Markus chamber with and without a tungsten eye shield in place. Dose planes were created by performing absolute film dosimetry using Gafchromic EBT3 film. Films were placed directly under the eye shield and analyzed to verify the transmission as well as quantify dose contributions to back and side scattered radiation. The backscatter radiation was also measured using TLDs. TLDs were placed on the entrance side of the eye shield. The dose due to backscatter from the tungsten was isolated by performing a measurement in the same geometry, using a 3D printed PMMA-like replica of the eye shields.

Results: Transmission through the eye shield was 1.5%, 2.5%, 5.7%, 17.3%, and 35.3% for 6, 9, 12, 16, 20 MeV respectively. For every energy, films were characterized by a high dose ring just on the outside of the dental acrylic coating of the eye shield. This hot spot was higher for low energy electrons (147% for 6 MeV vs. 135% for 20 MeV). The backscatter doses reported from the TLDs were also higher for low energies, with 6 MeV yielding a 117% hot spot compared to 109% for 20 MeV.

Conclusion: Films placed directly under a tungsten eye shield showed a substantial hot spot ring just outside the shield. This hot spot was larger for lower energies. Backscatter doses measured by TLDs showed a similar pattern vs. energy, though not nearly of the same magnitude.

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