## 1 Introduction  
Computed tomography (CT) scans with multi-detectors have become an essential tool in medical practice [1, 2]. However, there is an increasing trend in medical radiation exposure caused by CT imaging [3, 4]. Ionizing radiation is associated with cancer risk and thus must be subject to strict safety regulations [5]. In diagnostic and interventional medical exposure, the International Atomic Energy Agency (IAEA) refers to \"keeping the exposure of patients to the minimum necessary level to achieve the required diagnostic or interventional objectives\" [6].  
Over the last two decades, researchers have gained interest in developing new approaches to reduce radiation doses. For example, reducing the produced radiation/ milliampere-seconds (mAs), tube voltage/kilovoltage peak (kVp), and higher helical pitch will help to optimize patient radiation exposure as well as provide data that can be used for comparison between different CT scanner techniques [7,8]. Other dose parameters that can play a major role in optimizing patient radiation exposure include the computed tomography dose index volume (CTDIvol) and dose-length product (DLP) for complete examination [7,8].  
A comparison of CT doses with established diagnostic reference levels (DRLs) ensures CT exposures to be in line with the recommendations of international authorities, such as the IAEA, International Commission on Radiological Protection (ICRP), and European Commission [9]. These organizations encourage international governments to monitor DRL values continuously.  
The ICRP also advocates that each country should survey radiology practices, determine national DRLs to be used as exposure indicators, provide guidance for dose optimization, and ensure justification of appropriate doses for a given clinical indication [10,11]. Two essential techniques applied by automatic exposure control are automatic current modulation and automatic current selection, which can be separately enabled or combined [12]. These automatic exposure control techniques are based on mAs modulation to optimize variability in patient attenuation while providing a full scan with maintained image quality [12].  
Another essential concept in this era is the implementation of \"As Low As Reasonably Achievable\" to decrease unnecessary radiation exposure to patients [13]. A recent prospective observational study (2019) [14] demonstrated that the CT dose can be reduced by >50% without affecting image quality. The impact of dose reduction without affecting the quality of diagnostic yields in CT imaging can be observed with comparative strategies between default exposure parameters and a second group scanned with optimized parameters [15].  
The initiative to establish DRLs has been undertaken in the Kingdom of Saudi Arabia by the Saudi Food and Drug Authority to establish national diagnostic reference levels (NDRLs) [16]. There are several CT dose reduction techniques; however, few studies have explored optimal dose estimates using multiple exposure quantities.  
Additionally, the ICRP 135 report [17] was used as a guide to address contradictions related to the terminology used at that time, for example, the determinants of DRL values, the renewal of those values, and the application of the DRL concept to emerging imaging technologies.  
Therefore, this study aimed to optimize CT examination protocols to lower patients' organ radiation exposure during head, chest, abdomen, and pelvis CT examinations in our facility and to establish our optimized institutional DRLs as a benchmark that will enable us to correlate with NDRLs in the Kingdom of Saudi Arabia [16] and adhere to international guidelines for radiation exposure.