## 2 Materials and Methods
### High Energy LINAC Procedure  
The solid water phantom and the ionization chamber was set up on the bed of the linear accelerator (LINAC) machine. Then, the machine was set with 6 MV photon energy set and a varied prescribed dose ranging from 100 MU to 500 MU. Next, using the same energy and potential difference in electrometer of IC, experiments were started by setting the prescribed doses of 100 MU, 200 MU, 300 MU, 400 MU, and 500 MU in five different irradiation processes respectively to acquire the absorbed radiation doses. Afterwards, the irradiation processes on the expired EBT3 films were performed where film samples were placed at their depth in a solid water phantom, which provides the maximum dose, \(d_{max}\). IC was removed from the solid water phantom and one piece of the film sample was placed at the exact position of the IC, which is inside the prepared hole within the water phantom. Post-irradiated films were put inside black envelopes to avoid contamination from ambient light. Next, the irradiation processes were performed by replacing new film samples and repeating the previous steps. For electron beam experiment, the same solid water phantom and ionization chamber was set up on bed of LINAC machine and an electron applicator was installed on the collimator. Then, the machine was warmed up using the prescribed dose of 200 MU, energy 6 MeV set in the system, and a potential difference of 300 V in the electrometer of IC. Next, the steps were repeated as for the X-ray experiment above.  
After all the expired EBT3 film pieces had been irradiated to different radiation sources, absorbance measurements of every exposed expired EBT3 film were performed using an Ocean Optics Jaz spectrometer. The spectrometer covers the wavelengths from 200 to 1100 nm. The light source used in the spectroscopy setup was a tungsten halogen lamp (HL-2000) with spectral emission between 360 and 2500 nm and a color temperature of 2960 K. The Jaz spectrometer was connected to a tungsten halogen lamp via cuvette holder and attenuator by optical fiber. The expired EBT3 film was placed in the cuvette holder. The function of the attenuator is to reduce or increase the intensity of light from the halogen lamp in the unit counts. Before beginning with the measurements, the spectrometer was turned on, and the lamps were allowed to warm up for appropriate periods of time to be stabilized. The output was shown on a monitor screen using the SpectraSuite software. The system was calibrated using an unexposed film. An unexposed film sample was placed in the cuvette holder to be used as a reference and for calibration purposes, and then the important configurations were set. The integration time, scan to average, and boxcar width were set to 3 ms, 30, and 1 respectively. After setting the important configurations, a card was slit into tungsten halogen lamp to prevent light from passing through and directly eliminating the dark current in the software. The card was taken out from tungsten halogen lamp to let the light pass through again. The absorbance with the letter 'A' was selected in the software and the output showed 0 absorbance corresponding to the unexposed film. After the calibration process, the absorbance measurement of each exposed film sample was performed and saved. The best wavelength was observed based on the highest peak absorption spectrum.  
Finally, fifteen exposed and one unexposed film sample were scanned together using an Epson scanner (manufacturer). The configuration for scan was set to 600 dpi for optical resolution and an image color of 48 bits. The scanned image was saved in TIFF format. The image scanned was analyzed using ImageJ software. Red channel filtering was selected. Measurement of the mean gray value for one piece of the film sample was set by taking into account their values of standard deviation of mean gray value. The result was recorded.