Optical spectral analysis of radiochromic films irradiated with radiation therapy beams

Radiochromic films, owing to their high spatial resolution, are well-suited for radiation therapy dosimetry and quality assurance purposes. However, their spectroscopic response to radiotherapy beams has not been comprehensively investigated, except for a limited subset of beam qualities. In this work, we explore the spectral response of the EBT3 and EBT-XD radiochromic film models to different clinical radiation beam qualities including photons and protons. The spectral response of EBT3 and EBT-XD films showed two peaks at 585 nm and 635 nm for both photon and proton irradiation. Beyond a certain batch- and model-dependent dose threshold a saturation behavior was observed in the primary absorption peak. For beam qualities studied in this work, the spectral response of proton-irradiated films showed a systematic under-response compared to their photon-irradiated counterparts in both EBT-3 and EBT-XD radiochromic films models.