# Factors Affecting Implementation of Radiological Protection Aspects of Imaging in Radiotherapy
## 3 Results
### Imaging during the Treatment Cycle  
The purpose of imaging during the radiotherapy treatment cycle is to align the treatment beam precisely with the targeted tumour and deliver the radiation treatment as accurately as possible. Patient positioning accuracy with IGRT varies, depending on the treatment site, prescription, PTV margin, treatment delivery technique, and immobilization method. A typical set of clinical tolerance for daily alignment ranges from \(\sim\)10 mm for standard 3D breast treatment (planar MV and kV imaging), down to a few mm for IMRT treatments (3D CBCT imaging), and to sub-mm for intracranial high-dose stereotactic radiosurgery cases [17; 18]. The ICRP Task Group 116 report aims to deal with radiological protection aspects of IGRT and--after appropriate patient selection--there are four areas  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Country**} & \multirow{2}{*}{**HDI at Time of Survey**} & \multirow{2}{*}{\begin{tabular}{c} **No. of** \\ **Radiotherapy** \\ **Centres in Survey** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Proportion of** \\ **Radiotherapy** \\ **Centres in Survey** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **No. of Linacs in** \\ **Survey** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Median No. of** \\ **Linacs per** \\ **Radiotherapy** \\ **Centre** \\ \end{tabular} } \\ \hline Germany & 0.947 & 10 & 3.4 & 26 & 2.5 \\ Australasia & 0.944 & 12 & 10.8 & 55 & 3 \\ USA & 0.926 & 30 & 1.2 & 143 & 4 \\ Cyprus & 0.887 & 2 & 100 & 5 & 2.5 \\ Saudi Arabia & 0.854 & 4 & 28.6 & 16 & 2.5 \\ Malaysia & 0.81 & 7 & 23.9 & 9 & 1 \\ Colombia & 0.767 & 14 & 24.1 & 24 & 2 \\ Algeria & 0.748 & 9 & 56.2 & 24 & 3 \\ Egypt & 0.707 & 9 & 12.5 & 17 & 1 \\ Total & - & 97 & - & 319 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Data on radiotherapy centres completing the questionnaire for each country [14].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Country**} & \multirow{2}{*}{**CBCT (\%)**} & \multirow{2}{*}{**kV Planar (\%)**} & \multirow{2}{*}{**MV Planar (\%)**} & \multirow{2}{*}{**MRI (\%)**} & \multirow{2}{*}{
\begin{tabular}{c} **Optical** \\ **Surface** \\ **Guidance (\%)** \\ \end{tabular} } & \multirow{2}{*}{**Ultrasound (\%)**} \\ \hline Germany & 100 & 60 & 50 & 10 & 60 & 30 \\ Australasia & 100 & 83 & 42 & 17 & 25 & 58 \\ USA & 100 & 97 & 70 & 17 & 73 & 17 \\ Cyprus & 100 & 100 & 100 & 0 & 50 & 0 \\ Saudi Arabia & 100 & 50 & 25 & 25 & 0 & 50 \\ Malaysia & 100 & 71 & 57 & 0 & 29 & 0 \\ Colombia & 86 & 50 & 57 & 0 & 14 & 7 \\ Algeria & 89 & 67 & 56 & 0 & 0 & 11 \\ Egypt & 22 & 0 & 100 & 0 & 11 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Percentages of radiotherapy centres in each country using different imaging modalities to check patient position during treatment [14].  
involved in the choices relating to optimization of radiological protection. These are: the imaging modalities used, the frequency of imaging, the image acquisition parameters determining the quality of the image, and the volume of surrounding normal tissue included in the images.