Room: Exhibit Hall | Forum 7
Purpose: The purpose of this study was to investigate the spectral response of EBT3 radiochromic films to proton therapy beams. Dose, dose rate, and interbatch dependencies on the spectral response of the films were studied. A spectral comparison between films irradiated with proton, photon and electron clinical beam was also performed.
Methods: Pieces of EBT3 radiochromic films, placed between layers of solid water phantoms, were irradiated with proton beam at dose levels between 0.25 and 10 Gy using a Mevion S250 passive scattering proton therapy machine. For each film sample, the net absorbance spectrum was measured as a function of wavelength in the wavelength range of 400â€“800 nm using a fiberâ€?coupled spectrometer and a broadband light source.
Results: The net absorbance spectrum of proton-irradiated EBT3 films showed two absorption bands centered on 636 nm (primary) and 585 nm (secondary), characteristic of that of photon- and electron-irradiated films. For doses above a certain batch-dependent threshold the primary absorption band tends to flatten and â€œsplitâ€? into two bands. No significant change was observed in the absorption spectra with the dose rate. Slight differences in the spectral shape and absorbance value were observed in the film samples irradiated with the same dose from different batches. Compared to photons and electrons, the proton-irradiated film samples showed a systematically lower net absorbance value indicating possible linear energy transfer (LET) dependency.
Conclusion: The spectral shape of the EBT3 radiochromic films irradiated with proton beams varies with dose level and batch. While photon and electron irradiation on the films produces same spectral response, the absorption spectrum of proton-irradiated films shows lower net absorbance.
Funding Support, Disclosures, and Conflict of Interest: This work is supported by the Department of Radiation Oncology of the Washington University School of Medicine.