## 2 Materials and Methods  
We estimated the AGD of 247 women who underwent mammographic X-ray examinations at eight clinics in Sudan. The women underwent symptomatic and screening mammography. The different types of equipment investigated included direct digital radiography (DR), computed radiography, and screen-film (SF) radiography. Table 1 lists information regarding the studied mammography equipment. For dose assessment in digital mammography devices, patient exposure parameters were retrospectively extracted from the Digital Imaging and Communications in Medicine header. In the SF devices, the required data were registered in special forms by a technologist during the examination. Our institutional ethic committee approved this study. Due to the retrospective nature of the data collection, the requirement for individual patient consent was waived for this study. The workload for the mammography system ranged from 10 to 20 patients per week.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Clinic** & **Make/Model** & \begin{tabular}{c} **County of** \\ **Origin** \\ \end{tabular} & **Modality** & **Target/Filter** & **AEC** & \begin{tabular}{c} **Year of** \\ **Installation** \\ \end{tabular} & \begin{tabular}{c} **Institution** \\ **Type** \\ \end{tabular} \\ \hline \multicolumn{8}{c}{SF mammography} \\ \hline M3 & Philips & The Netherlands & \begin{tabular}{c} Kodak Mini R2 \\ cassette/Mini R2 2000 screen \\ \end{tabular} & Mo/Mo & No & 2007 & Private \\ \hline M4 & Lilyum/Metaltronica & Italy & \begin{tabular}{c} Kodak Mini R2 \\ cassette/Mini \\ R2 2190 screen \\ \end{tabular} & Mo/Mo & No & 2010 & Private \\ \hline \multicolumn{8}{c}{Digital mammography (CR \& DR)} \\ \hline M1 & Giotto & Italy & CR/Fuj IP & Mo/Mo & No & 2010 & Government \\ \hline M2 & GE & USA & DR/FP & \begin{tabular}{c} Rh/Rh, \\ Mo/Rh, \\ Mo/Mo \\ \end{tabular} & AEC & 2012 & Government \\ \hline M5 & SIEMENS/Mammomat C/ & Germany & \begin{tabular}{c} CR/Fuj IP \\ cassette type \\ CC \\ \end{tabular} & Mo-Rh & No & 2012 & Private \\ \hline M6 & Lilyum/Metaltronica & Italy & \begin{tabular}{c} CR/Fuj IP \\ cassette type \\ CH \\ \end{tabular} & Mo-Mo & AEC & 2014 & Private \\ \hline M7 & Philips & \
\begin{tabular}{c} The \\ Netherlands \\ \end{tabular} & CR & Mo/Mo & AEC & 2014 & Government \\ \hline M8 & Neusoft/NM-GA & China &
\begin{tabular}{c} DR/amorphous \\ selenium FP \\ \end{tabular} & Ag-Rh & AEC & 2016 & Government \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mammography equipment information.  
In mammography, the radiation dose is determined in terms of AGD, the recommended dosimetric quantitative value of interest for radiation risk assessments in mammography (NCRP 1987, 1996) [23]. For each breast, the AGD was estimated for two views: the craniocaudal (CC; head to foot) and mediolateral oblique (MLO; from the middle of the chest out to the side of the body with the X-ray tube placed at an angle) views.  
In each of the CC and MLO views of the breast, the following parameters were recorded: compressed breast thickness (CBT), target and filtration material, tube peak kilovoltage (kVp), and exposure current-time product (mAs). Other machine parameters, such as the beam half-value layer (HVL) and radiation output, were measured. The study included only women over 30 years of age with breast thickness between 20 and 80 mm.