Radioprotection No 59-1 | Page 49

S . Semghouli et al .: Radioprotection 2024 , 59 ( 1 ), 42 – 49 43

Table 1 . Specifications of the machines used for data collection .

and Leng , 2020 ; Wang et al ., 2020 ). However , the concept of Diagnostic Reference Level ( DRL ) was introduced in the early 1990s in Publication 60 ( ICRP , 1991 ) of the International Commission on Radiological Protection ( ICRP ) to apply the principle of optimization to patient exposure in the field of medical imaging . The implementation of DRLs was recommended in Publication 73 " Radiological Protection and Safety in Medicine " ( ICRP , 1977 ), and then made mandatory in 1997 in European Union member states by Directive 97 / 43 / Euratom . This led some countries to publish its first decree on diagnostic reference levels in radiology and nuclear medicine . Diagnostic reference levels , which are a tool for optimization , should not be regarded as " dose limits " or " optimal doses ". In practice , these levels are established for standardized examinations and typical patients . They should not be exceeded , on average for a given facility and examination , without justification during routine practical procedures . DRLs are dosimetric indicators of the quality of practice , designed to identify and monitor situations requiring corrective action , and to quantify the effectiveness of an optimization approach . In principle , managers of conventional radiology , CT and nuclear medicine facilities are required to carry out an annual assessment of the doses delivered to their patients during diagnostic procedures . Analysis of the data , by comparing their average value with the DRL , should enable professionals to situate their practices in relation to a national benchmark , and to take corrective action in the event of unjustified excesses . Indeed , exceeding the national benchmark could be considered as a potential sign of malfunction during one of the stages of the process of carrying out the imaging scan . The DRL is a warning indicator provides guidance for dose optimization , and ensures justification of appropriate doses for a given clinical indication . In this way , a facility with recent equipment offering considerable latitude in terms of optimization will be able to apply the principle of dose optimization as effectively as possible , by setting itself a more ambitious objective than the current DRL .

Many initiatives have been undertaken in Morocco focusing on radiation exposure during CT procedures . Monte Carlo methods were used to estimate patient radiation exposure and foetal dose during CT pelvimetry ( Aabid et al ., 2023a , 2023b ). Assessment of physicians ’ knowledge of patient radiation protection when prescribing CT scans ( Amaoui et al ., 2023 ), and establishment of local diagnostic reference levels for several CT procedures , such as cerebral ( Semghouli et al ., 2022a ), pelvimetry ( Semghouli et al ., 2020 ), chest and abdomen ( Mansouri et al ., 2022 ), thoraco-abdominal and lumbar ( Amaoui et al ., 2019 ; Semghouli et al ., 2022c ). Other research has been conducted to assess the risks of radiation exposure to patients following brain ( Abid et al ., 2019a ; Semghouli et al ., 2022b ) CT scan examinations . The absence of a prior study on national practices for optimizing abdominopelvic tomography prompted us to undertake this study . This investigation aimed to evaluate radiation exposure doses for adult patients , then to establish the local diagnostic reference level ( DRL ) for the five university hospitals in Morocco as well as to propose a national DRL .

2 Materials and methods

2.1 Data collection

This study was based on data collected during abdominopelvic CT procedures in five Moroccan university health centers , namely UHC-1 , UHC-2 , UHC-3 , UHC-4and UHC-5 . All are public hospitals serving and providing diagnostic services to a large population in and around the abovementioned cities . Table 1 summarizes the data for the health centers included in this study , along with specifications relating to the CT scanners installed in these centers , such as manufacturer , type and date of installation .

Data were collected for 300 adult patients at a rate of 60 CT examinations per hospital between February 2023 until June 2023 . For patients undergoing abdominopelvic CT examinations , patient data ( age , sex and weight ), exposure parameters ( tube voltage ( kV ), tube current ( mAs ), rotation time ( s ), pitch value ) and dosimetric parameters ( dose-length product ( DLP ) and CT dose index volume ( CTDI vol )) were collected .

2.2 Dose calculation

The methodology described in Report 135 ( Vañó et al ., 2017 ) of the International Commission on Radiological Protection ( ICRP ) was followed to calculate the dosimetric parameters . The Computed Tomography Dose Index ( CTDI ( mGy )) is a standardized measure of the radiation dose resulting from a CT scanner and is essential for comparing the radiation power of different CT scanners . CTDI 100 ( mGy ) ( represents the linear dose distribution measured on a 100 mm long by a pencil-shaped ionization chamber ) and CTDI w ( single slice dose weighted average ) were used in the past . While for currently used helical scanners , the CTDI vol parameter is the most commonly used index .

The dosimetry parameters ’ CTDI w , CTDI vol , DLP ( mGy . cm ) and effective dose ED ( mSv ) can be calculated using the following equations ( ICRP , 2001 , McNitt-Gray , 2002 ):