Spectral analysis of the <scp>EBT</scp> 3 radiochromic films for clinical photon and electron beams

摘要： Purpose: To investigate the spectral response of the EBT3 radiochromic films to different beam qualities for radiation therapy dosimetry. Dose, dose rate, and inter-batch dependencies on the spectral response of the films are investigated as well. Methods: Pieces of EBT3 films placed between layers of solid water phantoms were irradiated with 6 and 15 MV photon beams, 6 and 10 MV-FFF photon beams, and 6 and 20 MeV electron beams at dose levels between 0.4-50 Gy. Net absorbance was measured as a function of wavelength from the spectra acquired in the wavelength range of 400-800 nm using a fiber-coupled spectrometer and broadband light source. Results: No significant change was observed in the absorption spectra of the EBT3 films irradiated with the same amount of dose using different beam qualities. Also, no spectral change with dose rate was observed. The measured net absorbance per Gy was independent of beam quality in the 1-50 Gy dose range. Slight differences in the spectral shape and absorption band positions were observed in film samples from different batches. The net absorbance spectra showed two absorption bands centered around 634-636 nm (primary) and 583-585 nm (secondary). However, depending on the film batch, for doses above a certain level the primary absorption band appears to “split” into two bands centered around ~624-628 and ~641-645 nm. Conclusions: The spectral shape of the EBT3 radiochromic films irradiated with photons (including FFF) and electron beams is beam quality and dose rate independent; however it varies with dose level, batch, and spectroscopy system used.