## 2 Materials and Methods  
All patients that were treated using VMAT and who underwent both NCCT and CCT sequentially during the same radiotherapy CT simulation session as part of their \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Site**} & \multirow{2}{*}{**Study Author**} & \multirow{2}{*}{**No. of Patients**} & \multirow{2}{*}{**Technique**} & \multicolumn{2}{c}{**Clinically Significant (S) or Not (NS)**} \\ \cline{5-8}  & & & & & & **Targets** & **Critical Structures** \\ \hline
**2001 * & Bladder & Weber et al. [27] & 5 & 3 DCRT & NS & NS \\ \hline
**2006** & Head and Neck & [PERSON] et al. [21] & 15 & IMRT & NS & NS \\ \hline
**2006** & [PERSON] & [PERSON] et al. [19] & 20 & 3 DCRT & NS & NA \\ \hline \multirow{4}{*}{**2007**} & Whole brain & & 5 & & NS & \\ \cline{2-8}  & Whole-neck & & 5 & & NS & \\ \cline{2-8}  & Mediastinum & [PERSON] et al. [16] & 5 & 3 DCRT & NS & NA \\ \cline{2-8}  & Whole-pelvis & & 5 & & NS & \\ \cline{2-8}  & Upper abdominal & & 6 & & S & \\ \hline
**2008** & Abdomen & [PERSON] et al. [13] & 6 & 3 DCRT & NS & S \\ \hline
**2008** * & Head and Neck & [PERSON] et al. [36] & 10 & IMRT & NS & NS \\ \hline
**2009** & Head and Neck & [PERSON] et al. [37] & 12 & 3 DCRT & NS & NS \\ \cline{2-8}  & Pelvis & & 8 & & NS & NS \\ \hline
**2009** & H&K/NTC & [PERSON] et al. [38] & 15 & IMRT & NS & NS \\ \hline
**2010** & Non-small cell lung cancer (NSCLC) & [PERSON] et al. [26] & 5 & IMRT & NS & NA \\ \cline{2-8}  & Lung and Esophagus & [PERSON] et al. [31] & 17 & 3 DCRT & NS & NS \\ \hline
**2012** & Lung and Esophagus & [PERSON] et al. [24] & 13 & IMRT & NS & NS, except Heart \\ \hline
**2013** * & Esophagus & [PERSON] et al. [24] & 9 & 3 DCRT & NS & NS, except Heart \\ \hline
**2013** & Non-small cell lung cancer (NSCLC) & [PERSON] et al. [55] & 9 & IMRT & NS & NS \\ \hline
**2013** * & Prostate & Gleeson [29] & 10 & 3 DCRT & NS & NS \\ \hline
**2014** & Esophagus & [PERSON] et al. [17] & 17 & 3 DCRT & S & NS \\ \hline
**2015** & Head and Neck & [PERSON] et al. [23] & 5 &
\begin{tabular}{c} VMAT and Helical \\ Tomictherapy \\ \end{tabular} & NS & NS \\ \hline
**2016** & Head and Neck & [PERSON] et al. [39] & 10 & VMAT & NS & NS \\ \hline
**2016** & Pevis & Heydatheydari et al. [22] & 6 & 3 DCRT & NS & NS \\ \hline
**2016** * & Prostate & [PERSON] et al. [30] & 10 & VMAT & S & S \\ \hline
**2017** * & [PERSON] & Aras et al. [28] & 5 & 3 DCRT & NS & NS \\ \hline \multirow{4}{*}{**2017**} & Head and Neck & & 1 & 3 DCRT & NS & NS \\ \cline{2-8}  & Head and Neck & & 5 & IMRT & NS & NS \\ \cline{2-8}  & & [PERSON] et al. [18] & 1 & 3 DCRT & NS & S (lower thoracic \\ \cline{2-8}  & Thoracic and Abdominal & [PERSON] et al. [18] & 24 & IMRT & NS & NS \\ \cline{2-8}  & & & 3 & 3 DCRT & NS & NS \\ \cline{2-8}  & Pelvis & & 9 & IMRT & NS & NS \\ \hline
**2019** * & Head and Neck & [PERSON] et al. [32] & 15 & VMAT & NS & NS \\ \hline
**2020** * & Esophagus & [PERSON] et al. [25] & 10 & VMAT & NS & NS \\ \hline
**2020** * & Pelvis & [PERSON] et al. [20] & 33 & VMAT & S & S \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Literature search summary for the effect of contrast agents on radiotherapy dose calculations. Upper subscripts denote correction method used to overcome the effect of contrast material. *: resetting structure density to water equivalent density; *: changing structure density using structure density from diagnostic images for same structure; *: overriding the HU by other values; *: using virtual monochromatic images in DECT; *: using artificial intelligence to correct HU values; *: altering densities based on simulated CT images. normal clinical pathway were selected. This included all radiotherapy patients treated from January of 2011 to December of 2018 at the Comprehensive Cancer Center, King Fahad Medical City (KFMC).