## 3 Results
### Net ROD Measurement  
For this analysis method, all films samples were analyzed using ImageJ software to measure the mean gray value for every film sample after being scanned by the EPSON. Perfection V370 Photo scanner. Next, net ROD were calculated using Equation (6) and the results are presented in Table 6.  
\[\text{Net ROD}=\log\left(\text{P}_{\text{u}}/\text{P}_{\text{t}}\right) \tag{6}\]  
where P\({}_{\text{u}}\) denotes the pixel value of the reflected intensity via an unexposed film at the orientation in which the maximum pixel value is obtained, and P\({}_{\text{t}}\) denotes the pixel value of the reflected intensity at any other film orientation or irradiation level [23; 24]. From the analysis using ImageJ software, the mean gray value using red channel filtering was measured for each expired EBT3 film and the net ROD was calculated using Equation (6). The results were recorded and are shown below. Table 6 represents the net ROD value for every absorbed dose of three different sources of radiation. Figure 4 illustrates the pattern of the obtained results of the respective ROD. In terms of energy dependency, expired Gafchromic EBT3 film appeared to show the highest value for net ROD for high energy radiation. For instance, at absorbed dose of 1 Gy, the 6-MeV electron beam showed the highest value net ROD, which was 0.086, compared with radiography X-rays (90 kVp) obtained from linear analysis from Figure 4, which had a net ROD value of 0.043. The percentage difference of net ROD between these energies for the absorbed dose of 1-5 Gy was around 52% to 67%, which is very high as shown in Table 7. According to [PERSON] et al. [25], the film's response is weakly dependent on the energy of high-energy photon beams generally used in radiotherapy, regardless of color channel. Besides that, in another study from [PERSON] et al. [26], the differences between films were negligible with values less than 1% for doses up to 4 Gy. Therefore, with the high value of percentage difference obtained from this experiment, the expired EBT3 film response appeared to be nearly dependent on radiation energy used and against previous results from the literature. This probably happened due to the different experimental set up and the type of radiation detector used. The discrepancies on the absorbed dose measurement might affect the analysis of net ROD on the sample for 90-kVp X-ray as shown in Figure 5. \begin{table}
\begin{tabular}{c c c} \hline
**Wavelength (nm)** & \(R^{2}\) **(\%)** & **RMSE (Gy)** \\ \hline
541.48, 561.11, 600.28 & 89.3 & 0.585 \\
650.79, 654.10, 660.37 & 85.2 & 0.688 \\
600.28, 650.79, 654.10 & 85.4 & 0.682 \\ \hline \end{tabular}
\end{table} 
Table 4: Results of multiple linear regression technique using selected wavelengths for all experiments. \begin{table}
\begin{tabular}{c c c} \hline
**Wavelength (nm)** & \(R^{2}\) **(\%)** & **RMSE (Gy)** \\ \hline
541.48, 561.11, 600.28 & 97.2 & 0.350 \\
650.79, 654.10, 660.37 & 96.9 & 0.364 \\
600.28, 650.79, 654.10 & 96.4 & 0.395 \\ \hline \end{tabular}
\end{table} 
Table 5: Results of multiple linear regression technique using selected wavelengths for the 6-MV photon beam and 6-MeV electron beam source. Figure 5 shows a comparison of net ROD for electron and photon irradiations. The obtained results showed close results for both radiation types and for the same doses. A previous study by [PERSON] et al. [8] showed that discrepancies remain less than 0.07% for doses below 350 cGy and increase slightly up to 0.1% for doses around 500 cGy. However, from this study, the percentage difference of net ROD between the 6-MV photon beam and 6-MeV electron beam at 1 Gy, 2 Gy, 3 Gy, and 4 Gy obtained values of 8.5%, 10.2%, 8.1%, and 7.3% respectively as shown in Table 7. At 5 Gy absorbed dose, the percentage difference of net ROD was the lowest, which is 1.0%, and showed no significant difference. The low combined percentage difference observed for the type of radiation dependence makes expired EBT3 suitable for dosimetry in various sources of radiation.