(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: To characterize spectral response of the EBT3 radiochromic films to megavoltage photon and electron beam irradiations for radiation therapy dosimetry.
Methods: Pieces of Gafchromic EBT3 films with 5 x 5 cm² size sandwiched between solid water phantom were irradiated using 6, 10 and 15 MV photon beam, and 6 and 20 MeV electron beam from a Varian TrueBeam™ linear accelerator. For a standards 10 x 10 cm² field 50, 100, 200, 1000, and 2000 MUs were delivered to the films. Absorption spectroscopy was performed using a fiber-coupled spectrometer in 400 to 800 nm spectral range with 0.43 nm resolution. A deuterium-tungsten halogen lamp was used as a light source. The output of the light source was collimated by using a converging lens to create a 1-cm diameter spot on the film sample. Another converging lens was used to collect the light passing through the film and couple that to the fiber.
Results: For all energies, the absorption spectra showed two absorption bands, the highest centered at ~635 nm and the other at ~585 nm. In contrast to previously published results for EBT3 films, the location of the bands was maintained for all doses and beam qualities. Additionally, three more bands centered around 560, 520, and 480nm were observed. The absorption spectrum in each case was decomposed into 11 Lorentzian components. For doses > 10 Gy the highest band in the absorption spectrum can be decomposed into bands at 641 and 628 nm.
Conclusion: The shape of the absorption spectra for electron beams remains similar to that of photons, and no apparent oversensitivity observed for electron beams. However, caution must be exercised when using a densitometer with a narrow beam for doses > 10 Gy due to “splitting� of the band centered at ~635 nm.
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