# Assessment of Imaging Protocol and Patients Radiation Exposure in Computed Tomography Colonography
## 3 Results and Discussion  
CTC dose was assessed for 55 patients presenting with a range of clinical indications, using two helical scanners and varying imaging protocols, as in Table 1. Similar exposure parameters were used for the CT machines, with slight change in the tube current-time product (mAs) and use of the adaptive statistical iterative reconstruction technique (ISRT). Both parameters (mAs and ISRT) impact the dose reduction during CT imaging while maintaining diagnosable images. The dose reduction is considered to be important, with radiogenic risk from the imaging procedure conservatively assumed to be linearly related with the dose received, other influencing factors being held constant (age, dose per procedure, organ sensitivity). CTC was performed for different clinical indications using four imaging protocols: supine and one decubitus, supine, two decubiti, auto tube current, and routine (manual), as illustrated in Table 2. The mean \(\pm\) SD, median, and range of (tube current (in mA) and (CTDI\({}_{\text{vol}}\) (in mGy) radiation dose has been calculated for two decubiti according to the imaging protocol. This variation in CT protocol results in an up to three-fold variation in patient-effective dose (Table 2). The effective dose from supine and two decubitus protocol CRC give the greatest value (31.6 mSv), exceeding that of the routine protocol (9.6 mSv). The effective dose in supine and two decubitus protocols are attributed to the high tube current used in this protocol, ranging from 300 to 450 mA per CTC procedure compared to the other three imaging protocols. The median and mean values for all patients groups are closely similar, suggesting asymmetrical distribution of the dose values for supine and two decubitus and routine CTC protocols. Conversely, for supine and one decubitus and auto tube current (mA) protocols, the dose values are skewed, with many CTDI\({}_{\text{vol}}\) (mGy) values at the higher end. Table 3 shows the image acquisition parameter and radiation dose values according to the manufacturer and the tube current mode. Automatic tube current modulation (ATCM) shows a significant increase in CTDI\({}_{\text{vol}}\) (mGy) (69%) and effective dose (mSv) (95%) than the manual tube current (Table 3). ATCM is established on the basis of attenuation of the radiation during image acquisition in order to adjust for disparities in patient anatomy while maintaining the image quality, reducing unnecessary exposure. In contrast, patient dose resulting from the application of ATCM are two times that of the standard protocol (Table 3). [PERSON] and [PERSON] [25] have reported that ATCM may reduce the dose during CT procedures by up to 60% while maintaining image quality. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Protocol**} & \multicolumn{2}{c}{**Tube Current (mA)**} & \multicolumn{2}{c}{**CTDI\({}_{\text{vol}}\) (mGy)**} & \multirow{2}{*}{**Effective Dose (MSV)**} \\ \cline{2-2} \cline{4-4}  & **Supine** & **Prone/Decubitus** & & & **Prone/Decubitus** \\ \hline Supine and one decubitus & 266.6 \(\pm\) 144 (100–350) & 266.6 \(\pm\) 144 (100–350) & 7.5 \(\pm\) 4 (2.8–9.8) & 7.5 \(\pm\) 4 (2.8–9.8) & 13 \(\pm\) 5.9 (6.1–16.8) \\ Supine and two decubitus & 375 \(\pm\) 106 (300–450) & 375 \(\pm\) 106 (300–450) & 13.4 \(\pm\) 1 (12.6–14.2) & 12.2 \(\pm\) 0.57 (11.8–12.6) & 31.6 \(\pm\) 0.38 (31.3–31.9) \\ Auto tube current (mA) & 253.1 \(\pm\) 63 (150–325) & 256.2 \(\pm\) 59 (150–325) & 11.2 \(\pm\) 5.2 (2.2–18.3) & 10.5 \(\pm\) 4.7 (2.1–16.5) & 18.7 \(\pm\) 9.9 (3.06–31.9) \\ Routine (manual) & 203 \(\pm\) 96.3 (100–440) & 202.2 \(\pm\) 96 (100–440) & 6.4 \(\pm\) 3.3 (2.7–15.5) & 6.51 \(\pm\) 3.9 (2.8–19.7) & 9.6 \(\pm\) 6 (2.1–26.7) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean \(\pm\) standard deviation (minimum \(-\) maximum) of (tube current (mA) and (CTDI\({}_{\text{vol}}\) (mGy) radiation dose is calculated for two decubitus according to the protocol.