Premium
SU‐E‐T‐298: Re‐Evaluation of Transmissions for a Commercial Tungsten Eye Shield in Electron Beams Using Radiochromic Film
Author(s) -
Wang Y,
Wu X,
MacPherson M
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612249
Subject(s) - shields , materials science , optics , imaging phantom , lens (geology) , tungsten , shield , enhanced data rates for gsm evolution , shielded cable , face shield , electromagnetic shielding , dosimetry , transmission (telecommunications) , beam (structure) , physics , nuclear medicine , medicine , telecommunications , computer science , composite material , health care , economic growth , economics , petrology , metallurgy , geology
Purpose: To re‐evaluate the transmission factors for a commercial tungsten eye shield used in 6 and 9 MeV electron beams based on the dose to the lens edge instead of the dose at the lens center using radiochromic film Methods: The eye shields have thickness of 2 or 3 mm with a 0.5 mm or 1 mm thick aluminum cap provided to reduce backscatter. The doses to the lens edge were measured at 3 mm depth below the shields and 5 mm from the central axis using Gafchromic® film. The doses were then normalized to the dose to dmax under the same setup without eye shields in place to generate the transmission factors. In contrast, the transmission factors referred by the manufacturer were determined with the lens dose measured at 3 mm depth along the central axis Results: The transmission factors are approximately 10 to 50% higher for a 6 MeV beam and 10 to 20% higher for a 9 MeV beam than the factors referred by the manufacturer. Transmissions are in general larger for smaller eye shields. In addition, one millimeter aluminum caps can increase the transmissions significantly for a 6 MeV beam. Transmission profiles at 3 mm depth in phantom are in the same shape regardless of their sizes. Transmissions at the edge of the shielded area at 3 mm depth were determined Conclusions: For internal eye shields transmission factors determined based on doses to lens edge can be significantly larger than the ones determined based on doses to the center of the lens. Transmission profiles reported here can aid dose estimation in some other situations. Relatively larger eye shields are suggested where clinically acceptable. The 0.5 mm aluminum caps are preferable in a 6 MeV beam.