###### Abstract  
The purpose of this study was to investigate the optical response of an expired External Beam Therapy (EBT3) film, which expired in 2018, using X-rays and electron beam doses. The film's optical responses were evaluated for its usability in measuring different radiation sources, energy, and absorbed doses ranging up to 5 Gy. Pieces of the expired EBT3 film were irradiated with 90 kV, 6 MV X-ray photons, and 6 MeV electron beam. The analysis was performed using the Jaz visible spectrometer and EPSON Perfection V370 Photo scanner to obtain the absorbance and the net relative optical density (ROD) of the film samples respectively. The results showed that spectroscopic measurements of the exposed expired EBT3 films under these radiation sources were able to produce primary secondary peaks at \(\lambda\) = 633.52 nm and \(\lambda\) = 582.3 nm respectively. The best wavelength subsets that presented the best MLR regression fitting for all experiments were 541.48 nm, 561.11 nm, and 600.28 nm. While, for the 6 MV photon and the 6 MeV electron beam they were 600.28 nm, 650.79 nm and 654.10 nm. In case of the irradiation with the 6 MV photon and the 6 MeV electron beam, expired EBT3 film showed no significant differences, which made it suitable for dosimetry in various sources of radiation. The individual calibration of radiation dose produces very high measurement accuracy with coefficient of determination, R\({}^{2}\) above 0.99 and root mean square of error, RMSE of 0.038 Gy, 0.113 Gy, and 0.115 Gy for films irradiated with 90 kVp X-rays, 6 MV photon beam, and 6 MeV electron beam respectively. Hence, from the results, the expired EBT3 film used in this study showed promising usability of expired EBT3 films beyond their prescribed expiry dates. colorimetry; expired EBT3; expiry date; visible spectroscopy 2022  
[PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]. characteristics should be addressed for more accurate findings, taking into consideration the sensitivity of such films to many factors, such as the radiation types and energies [9]. These films may be utilized not only to evaluate transverse beam profiles, but also to assess longitudinal (depth) dose distributions in both water and plastic phantoms [10; 11]. Accurate and correct descriptions of therapeutic beams need thorough examinations of the films' features, particularly those that are reliant on the films' reactions to the beams qualities (electron and photon beams), dose rates, and dosage values [12]. EBT3 films are designed for the measurements of absorbed doses of ionizing radiation. They are particularly suited for high-energy photons. The responses of EBT3 films have been shown to be batch-dependent, but energy-independent for large-voltage photon beams, including filter-free (FFF) and electron beams [13; 14; 15]. After the exposure of the EBT3 films to radiation sources, the films colors will gradually change from light green to darker colors under incremental exposures by ionizing radiation. Therefore, the color change can be one of the dosimetric characteristics for ionizing radiation studies [16; 17]. The purpose of this study was to look at the effectiveness of expired EBT3 films as well as the optical reactions of expired EBT3 films using visible spectroscopy analysis, and net reflective optical density (Net ROD); dose calculation algorithms can be invented as precise and accurate film-based dosimetry, and to check if they show any properties in response to a different source of radiation and energy value. Using visible spectroscopy analysis, dose calculation algorithms can be invented as precise and accurate film-based dosimetry. Therefore, the high-accuracy spectroscopy-based algorithms computed in measuring the color changes of expired EBT3 films in relation to the absorbed radiation dose may lead to the development of a single film-based dosimeter that can be calibrated for various types of ionizing radiation measurements.