## 4 Discussion  
Research has shown that the radiation dose in patients who underwent CT was the highest in diagnostic radiography [28]. Therefore, scattered X-ray from patient in CT also seemed to be high due to the considerable radiation dose used in CT. It is imperative to identify the radiation dose exposure of the medical staff members who are present in the CT room during examination, particularly the radiation exposure dose of eye lens, whose equivalent dose limit is being reduced is important. The highest personal dose equivalent of the medical staff was observed in head scan. This is firstly owing to the small distance between the iso-centre and eye. Second, it assumed to be attributed to the higher radiation dose in the scan protocol (i.e., high DLP). \(H_{\text{p}}\)(3) without Pb glasses in head scan was 0.44 \(\pm\) 0.05 mSv per examination. If a medical staff member engages in assistant action of head CT scan 46 times without Pb glasses, the radiation dose of the eye lens reaches a new dose limit of 20 mSv/y. A medical staff member frequently assists patient during radiation exposure from necessity; therefore, it is important for the staff member to wear Pb glasses. In the meantime, in the first place, it should be considered whether the assistant action is necessary in the clinical situation based on the concept of 'justification of practices'. The assistant action should be kept to the minimum. In this study, \(H_{\text{p}}\)(3) in the chest and upper abdomen scan were relatively low. Furthermore, when an injection of contrast media is monitored as assistant action at only an early timing (e.g., in bolus tracking method), radiation dose exposure of medical staff would be smaller due to the short time of assistant action and less amount of X-ray used in the method. However, it is never negligible; if examination is repeated in dynamic scan, etc. in the case of holding patient body, the radiation dose is simply added. Furthermore, if an examination is performed with higher radiation dose (i.e., high DLP), the amount of scattered X-ray radiation increases. Additionally, as described above, since the radiation dose exposure of medical staff with scattered X-ray in CT examination is high, the use of mobile radiation shielding screen should be also considered depending on the situation in the case of observation/supervision of patient, to reduce radiation dose of the whole body. The use of a dosimeter for eye lens is not widespread; therefore, it is challenging to evaluate \(H_{\text{p}}\)(3) in the current clinical situation. Personal dose equivalent (i.e., \(H_{\text{p}}\)(3), \(H_{\text{p}}\)(10) and \(H_{\text{p}}\)(0.07)) per air-absorbed dose depends on the photon energy [29]. Within this study, there was no distinguished difference between the measured value of \(H_{\text{p}}\)(3) without Pb glasses and \(H_{\text{p}}\)(10), \(H_{\text{p}}\)(0.07) outside a protective apron in assistant action during CT examination that is generally performed with a tube voltage of 120 kV; the difference was within 25%. Therefore, it may be possible to estimate the radiation dose of eye lens of medical staff using popular personal dosimeter for \(H_{\text{p}}\)(10) or \(H_{\text{p}}\)(0.07) measurement in CT \begin{table}
\begin{tabular}{c c} \hline \hline
**Body Site of Scan** & **Effective Dose of Medical Staff (mSv/exam)** \\ \hline Head & 0.087 \\ Chest & 0.026 \\ Upper abdomen & 0.015 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Estimated effective dose exposure of the medical staff in each scan. \begin{table}
\begin{tabular}{c c} \hline \hline
**Body Site of Scan** & **\(H_{\text{p}}\)(3) (mSv/DLP) 1** \\ \hline Head & 3.6 \(\times\) 10\({}^{-4}\) \\ Chest & 7.4 \(\times\)10\({}^{-4}\) \\ Upper abdomen & 7.3 \(\times\) 10\({}^{-4}\) \\ \hline \hline \end{tabular} \({}^{\dagger}\) The value of \(H_{\text{p}}\)(3) in chest and upper abdomen scan were normalised to that assuming the medical staff was positioned at 75 cm distance from the iso-centre.  
\end{table}