Room: ePoster Forums
Purpose: To compare spectral response of the EBT-XD and EBT3 radiochromic films to 6 MV photon and 6 MeV electron irradiations for radiation therapy dosimetry.
Methods: Gafchromic films EBT-XD and EBT3 were cut into small pieces and irradiated with a 6MV photon and 6 MeV electron beams inside solid water phantom. For a nominal 10 x10 cm2 field size at 100 cm source-surface distance, radiation doses from 0.5-50 Gy range was delivered at 600 MU/min. In order to measure the spectral response, the films were illuminated by a deuterium-tungsten halogen lamp and net absorption was determined in 400-800 nm spectral range using a fiber-coupled optical spectrometer.
Results: The net absorption spectra of the EBT-XD film showed two absorption bands centered at 635 nm and 585 nm, as was the case for the EBT3. However, for a given amount of dose, the EBT-XD showed lower net absorbance than the EBT3 film, both for 6 MV photon and 6 MeV electron beams. For 636 nm absorption band, the net absorbance in the EBT-XD film decreased to 64.5%, 26.7% and 12.2% for 0.5, 10.0 and 50.0 Gy, respectively. For 585 nm absorption band, the net absorbance drop was 68.1%, 47.6% and 14.4% at 0.5, 10.0 and 50.0 Gy respectively. Variations of < 1.5% (on average) were observed in the net absorbance for films irradiated either with 6 MV or 6 MeV electrons for both EBT-XD and EBT3 films.
Conclusion: The net absorption spectra of the EBT-XD films showed two absorption bands at the same spectral positions reported for EBT3 films. However, for the same dose level, the net absorbance in the former was lower than that in the latter indicating lower response of the former to megavoltage irradiations. The net absorption spectra are similar for both electron and photon beams.