## 3 Results
### Main Findings after Optimizing Radiation Doses Based on National NDRLs  
The average KV remained unchanged in all scanned body organs, with an average of 120 (\(p\) = 0.87). In the pre-optimization phase, the highest mAs were for head imaging, which was lowered to 190, whereas the lowest was for imaging of the abdomen/pelvis, which was lowered to 120 (\(p\) = 0.07). Likewise, in the pre-optimization phase, head imaging had the lowest pitch (0.9) while chest imaging had the highest (1.38; \(p\) = 0.87).  
Nonetheless, the scan length was the shortest in head imaging, which was lowered to 17.5; the longest abdomen/pelvis imaging was lowered to 43.0 (0.048). CTDIvol and DLP were the highest for head imaging, which increased to 45.61 and 788, respectively, compared to chest imaging, which decreased to 10.40 and 393, respectively (\(p\) = 0.034 and 0.047, respectively). ED was the lowest for head imaging, which increased post-optimization to 1.74, and the highest for abdomen/pelvis imaging, which decreased to 8.72 (\(p\) = 0.01) (Table 1; Figure 2).  
Table 2 displays the current study NDRLs in comparison with those in other organizations, whereas Table 3 compares the mean organ dose between this study and similar international studies from the literature.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{Exam} & \multicolumn{2}{c}{**Current Study**} & \multicolumn{2}{c}{**NDRL**} & \multirow{3}{*}{**Nigeria**} & \multirow{3}{*}{**ICRP**} & **US A** & & **Japan** & **EU** & **Greece** & **Egypt** & **UK** & **Italy** \\  & \multicolumn{2}{c}{**(2022)**} & & & **A Arabia** & **2018** & **2007** & **2016** & **2015** & **2014** & **2014** & **2016** & **2011** & **2020** \\ \cline{2-13}  & **Before** * & **After** **[**16**]** & & & & & & & & & & \\ \hline \multicolumn{11}{c}{CTDIvol (mGy)} \\ \hline
**Head** & 47 & 50 & 55 & 61 & 60 & 56 & 85 & 60 & 67 & 30 & 60 & 70 \\ \hline
**Abdomen** & 19 & 15 & 15 & 20 & 35 & 16 & 20 & 25 & 16 & 31 & 15 & 18 \\ \hline
**Chest** & 17 & 12 & 12 & 17 & 30 & 12 & 15 & 10 & 14 & 22 & 12 & 15 \\ \hline \multicolumn{11}{c}{**DLP (mGy.cm)**} \\ \hline
**Head** & 845 & 903 & 1077 & 1310 & 1050 & 962 & 1390 & 970 & 1055 & 1360 & 970 & 1300 \\ \hline
**Abdomen** & 773 & 685 & 886 & 1486 & 780 & 781 & 1000 & 745 & 760 & 1325 & 745 & 550 \\ \hline
**Chest** & 624 & 461 & 468 & 735 & 650 & 443 & 550 & 610 & 480 & 420 & 350 & 570 \\ \hline \hline \end{tabular}  
* Before applying the National Diagnostic Reference Level (i.e., pre-optimization with default parameters). ***
* **After applying National Diagnostic Reference Level (i.e., post optimization with optimized parameters). The dose quantities after optimization reflect the achievable doses (ADs) in our department. **Abbreviations:*
* DLP, dose-length product (mGy.cm); CTDIvol, volume computed tomography dose index (mGy).  
\end{table}
Table 2: Comparison between the current study results, National Diagnostic Reference Levels, and international studies.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Organ** & **Current Study** & **Tanzania 2006** & **UK 2011** & **ICRP 2007** \\  & **2022** & [34] & [32] & [11] \\ \hline Eye lens & 42.0 & 63.9 & - & 50 \\ \hline Breast & 24.6 & 26.1 & 21.4 & 112 \\ \hline Lung & 23.9 & 31.5 & 22.4 & 114 \\ \hline Liver & 16.4 & 34.1 & 20.4 & 30 \\ \hline Bladder & 18.6 & 28.8 & 23.2 & 43 \\ \hline Uterus & 22.4 & 26.5 & 25.0 & 26.0 \\ \hline Ovaries & 16.7 & 24.0 & 22.7 & 11 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison between the mean organ dose in the current study and similar international studies.