## 2 Materials and Methods
### Statistical Analysis  
Mean HU values, dose values, and volumes were measured using built in Eclipse tools and dose volume histograms (DVH); all 226 patients were included in the analysis. Data analysis was performed using the Statistical Package for Social Sciences (SPSS) version 25 (SPSS Inc., Chicago, IL, USA). Alpha level \(p\)-value of less than 0.05 was considered statistically significant. The statistical analysis workflow is shown in Figure 1, and is divided into three steps:  
1. Normality test (Shapiro-Wilk test) that shows whether a dataset is distributed normally or exhibits a non-normal distribution [40]. 2. Mann-Whitney-Wilcoxon test to evaluate the differences between two independent non-normal distributions [41]. 3. Student's \(t\)-test to evaluate the difference between two paired independent normal distributions [42]. In the case of a group of less than three patients where normality test is not applicable, nonparametric related-samples Wilcoxon signed rank test was used. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline
**Site** & \multicolumn{3}{c}{**Thyroid**} & \multicolumn{3}{c}{**Mediastinum**} & \multicolumn{3}{c}{**Lung**} & \multicolumn{3}{c}{**Esophagus**} & \multicolumn{3}{c}{**NHL**} \\ \hline Organ \(\mid\)Value & HU & D\({}_{\text{max}}\) & D\({}_{\text{avg}}\) & HU & D\({}_{\text{max}}\) & D\({}_{\text{avg}}\) & HU & D\({}_{\text{max}}\) & D\({}_{\text{avg}}\) & HU & D\({}_{\text{max}}\) & D\({}_{\text{avg}}\) & HU & D\({}_{\text{max}}\) & D\({}_{\text{avg}}\) \\ Esophagus & YES & NO & NO & YES & NO & YES & NO & YES & NO & YES & NO & YES & NO & NO & & & \\ Heart & NO & NO & NO & NO & NO & NO & YES & NO & NO & YES & YES & NO & YES & NO & YES & YES \\ Left Kidney & & & & & & & & & & & & & & & YES & YES & NO & NO & & \\ Left Lens & & & & & & & & & & & & & & YES & YES & YES & & & \\ Left Lung & NO & NO & YES & NO & YES & YES & YES & YES & NO & YES & NO & NO & YES & YES & YES \\ Liver & & & & & & & & & & & & & & & YES & YES & YES & \\ Right Kidney & & & & & & & & & & & & & & & YES & YES & YES & \\ Right Lens & & NO & YES & NO & NO & YES & NO & YES & NO & NO & YES & NO & NO & YES & NO & YES & YES \\ Small Intestine & & & & & & & & & & & & & & YES & NO & NO & YES & YES \\ Spinal Cord & YES & NO & NO & YES & YES & NO & NO & NO & NO & YES & YES & NO & NO & YES & YES & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of statistical analysis results for critical structures in chest. “YES” indicates statistically significant difference in CT number (HU), maximum dose (D\({}_{\text{max}}\)), and mean dose (D\({}_{\text{avg}}\)) values between NCCT and CCT images, and “NO” is vice versa. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Site** & \multicolumn{3}{c}{**Brain**} & \multicolumn{3}{c}{**Nasopharynxx**} & \multicolumn{3}{c}{**Tongue**} \\ \hline Mandible & & & & & YES & YES & YES & YES & NO & NO & YES \\ Optic Chiasm & YES & YES & YES & YES & YES & YES & NO & & & & & \\ Oral Cavity & & & & & YES & YES & YES & YES & & & & & \\ Right Brachial Plexus & & & & & YES & NO & YES & & & & & \\ Right Cochlea & NO & YES & YES & YES & NO & YES & & & & & & \\ Right Eye & YES & YES & YES & YES & YES & YES & & & & & & \\ Right Lens & NO & NO & NO & YES & YES & YES & & & & & & \\ Right Optic Nerve & YES & YES & YES & YES & NO & NO & & & & & \\ Right Parotid & & & & & YES & YES & YES & YES & NO & & & & \\ Spinal Cord & & & & & YES & NO & NO & & & YES & NO & NO & NO & NO \\ \hline \hline \end{tabular}
\end{table}