Volume 57, Number 1, January-March 2022
|Page(s)||61 - 66|
|Published online||12 January 2022|
Establishing local diagnostic reference levels for adult computed tomography in Morocco
Ibn Tofail University, Faculty of Sciences, Department of Physics, Laboratory of Materials and Subatomic Physics,
P.O. Box 133,
2 Moulay Ismail University, Faculty of Sciences, Physical Sciences and Engineering, P.O. Box 11201, Zitoune Meknès, Morocco
* Corresponding author: firstname.lastname@example.org
Accepted: 17 December 2021
In Morocco, the radiation doses received by adult patients are increasing due to the number of CT examinations performed and the larger number of computed tomography (CT) scanners installed. The aim of this study was to evaluate the radiation doses received by patients for the most common adult CT examinations in order to establish local diagnostic reference levels (DRLs). Data from 1016 adult patients were collected during 3 months from four Moroccan hospitals. Dose length product (DLP) and volumetric computed tomography dose index (CTDIvol) were evaluated by determining the 75th percentile as diagnostic reference levels for the most common examinations including head, chest and abdomen. The DRL for each examination was compared with other studies. The established DRLs in Morocco in terms of CTDIvol were 57.4, 12.3 and 10.9 for CT examinations of the head, chest, abdomen, respectively. For DLP, they were 1020, 632 and 714, respectively. These established DRLs for CTDIvol were almost similar to the UK DRLs at all examinations, higher than the Egyptian DRLs and lower than the Japanese DRLs at the head CT examination, lower than the DRLs from Egypt and Japan at the CT abdomen examination. In terms of DLP, the DRLs were higher than those of the British studies, lower than those of the Egyptian and Japanese studies at the head CT examination were higher at chest CT and lower at abdominal CT than those of all selected studies. The higher level of established DRLs in our study demonstrates the requirement of an optimization process while keeping a good image quality for a reliable diagnosis.
Key words: DRL / CTDI / DLP / computed tomography
© SFRP, 2022
Computed tomography (CT) is a medical imaging technique that is continually evolving and improving using innovative and advanced technologies. Since the introduction of the first clinical CT scanners in 1972 several studies have reported an increase in the number of CT scans performed on adult patients (AlNaemi et al., 2020; Wachabauer et al., 2020; Garba et al., 2021). In 2017, 45.4% of the French population underwent diagnostic medical imaging procedures one or more times. Only a small percentage of patients (but representing several hundred thousand patients) combined multiple CT examinations, leading to high effective doses, potentially exceeding 100 mSv (IRSN and ExPRI Study Report, 2017).
Nowadays, Morocco has developed a medical imaging infrastructure with more than 424 radiology centers and 360 CT scanners (Saikouk et al., 2019), Which requires regular controls to evaluate the image quality and ensure the radioprotection of patients (Quality Assurance for Computed Tomography by IAEA, 2012). In terms of patient exposure dose, CT medical imaging procedures in diagnostic radiology provide in general higher doses than other imaging procedures (Alkhorayef et al., 2019; Mkimel et al., 2019). These high doses can lead to genetic mutations and radiation-induced cancers in the long term Evaluation of radiation risks during CT brain procedures for adults Evaluation of radiation risks during CT brain procedures for adults Evaluation of radiation risks during CT brain procedures for adults (AAPM Reports no.096, 2008; Semghouli et al., 2019).
In order to reduce these risks, it is recommended to implement the principles of radiation protection as described by the International Commission on Radiological Protection (ICRP) including justification and optimization (ICRP Publication 103, 2007). Justification is one of the fundamental principles of radiation protection meaning that the benefit to the patient due to the exposure to ionizing radiation must outweigh its potential harm (Vawda et al., 2015; Vañó et al., 2017). If radiation is justified, examinations must be optimized such that the dose is as low as reasonably achievable, by minimizing the dose of radiation received by patients, while maintaining good image quality (Khoramian et al., 2019; El Mansouri et al., 2021).
Diagnostic reference levels (DRLs) are an important optimization tool (Vassileva and Rehani, 2015), which was introduced by the ICRP in 1996, as a dosimetric indicator to evaluate the performance of equipment and procedures in terms of doses delivered to patients (Vañó et al., 2017). These DRLs are therefore an effective way to protect patients exposed to ionizing radiation during diagnostic procedures such as conventional radiology, Computed tomography, nuclear medicine or interventional examinations, and are a reference value for comparing practices. In addition, DRLs are neither exposure limits nor optimal values and are not applicable to individual exposures.
DRLs for CT examinations are determined for the dose indicators CTDIvol (volume Computed Tomography Dose Index) and DLP (Dose Length Product) at the 75th percentile (3rd quartile) of the dose distribution (Kanal et al., 2017). In Morocco, too limited studies have established DRLs (Aabid et al., 2019). Nevertheless, they are successfully implemented in Europe, the United States and other developed countries (Nyathi and Shivambu, 2019). According to a report published in 2020 by the Institute of Radioprotection and Nuclear Safety (IRSN), the established DRLs for CTDIvol were 46, 9.5, and 13 mGy for the head, chest, and abdomen/pelvis, respectively, whereas the DLPs for the respective protocols were 850, 350 and 625 mGy.cm (IRSN Report, 2020).
Thus, the purpose of this study is to investigate the doses delivered to patients during the most common adult CT examinations, which include the head, chest and abdomen, and subsequently to establish local DRLs in Morocco.
Dosimetric CT data were collected during 3 months, from the 1st of April to the 30th of June 2021, from 4 CT scanners installed in 4 Moroccan hospitals. These data have been collected retrospectively for three hospitals and prospectively for the 4th hospital, with almost 250 examinations in each hospital. The four CT scanners were from several different companies, of different brands and models, and are all of 16-slice (Tab. 1).
One thousand and sixteen data have been collected from adult patients who underwent different routine CT examinations, including 309 head examinations, 382 chest examinations and 325 abdominal examinations. Details of the collected data of patients are presented in Table 2 according to the age and sex. In addition, the collected data included: tube voltage (kV), tube current time product (mAs), pitch, as well as mean CTDIvol (mGy) and DLP per examination (mGy.cm) (Tab. 3). Automatic tube current modulation, type of scan (helical/axial), use of contrast media and other parameters are not discussed in this study.
CT scanners characteristics per hospital.
Demographic distributions of the study population.
Analysis by examination type, use of different exposure parameters as well as CTDIvol and DLP.
The Collected data from adult patients have been evaluated using the software (IBM SPSS statistics version 26), as quantitative variables, which are indicated with arithmetic means, median (50th percentile) and third quartile (75th percentile). Furthermore, the established DRLs in Morocco have been compared to those of other countries in United Kingdom, Japan and Egypt (Health England Public, 2011; DRLs in Japan, 2015; Salama et al., 2017).
In this study, three examinations have been evaluated including the head, chest and abdomen, which represented more than half of all CT examinations performed in the four Moroccan hospitals. The International Commission on Radiological Protection (ICRP) has indicated that diagnostic reference levels are set for routine radiological examinations; therefore, non-routine examinations have been omitted from this evaluation.
Table 3 shows the main exposure parameters applied in all evaluated CT examinations including tube voltage (kV), tube current time product (mAs), pitch as well as CTDIvol and DLP. The minimum and maximum values of these parameters were 120 KV and 140 KV for the tube voltage, 72 mAs and 230 mAs for the tube current-time product and 0.76 and 1.5 for the pitch. The collected minimum value of CTDIvol for all CT examinations was 5.6 mGy of the abdomen examination and 59 mGy was the maximum value of the head examination. As for the DLP, 130 mGy.cm was the minimum value of the chest examination and 1254 mGy.cm was the maximum value collected of the head examination.
In addition, the mean, median and 75th percentile values of the dosimetric indicators in terms of CTDIvol and DLP of each CT examination are summarized in Table 4. The median CTDIvol values were 56.4, 9.7, and 9.2 for the head, chest and abdomen CT examinations respectively. Regarding DLPs, the median values were 980, 282, and 517.5 for CT examinations of the head, chest and abdomen respectively. As a result, the local DRls are presented graphically in Figures 1–6 and defined as the 75th percentiles of the CTDIvol and DLP distribution.
Analysis by examination CT of Mean, Median and 75th percentile for CTDIvol and DLP.
Despite the large number of CT scanners installed in Morocco, limited studies have established diagnostic reference levels for adult CT examinations. The Established DRLs of this study have been compared with other DRLs conducted in the United Kingdom in 2014 (Health England Public, 2011), that of Japan in 2015 (DRLs in Japan, 2015) and that of Egypt in 2016 (Salama et al., 2017). Table 5 shows the comparison of the local DRLs with the selected studies.
The evaluation for head examination has shown that the 75th percentile of CTDIvol was higher than that of Egypt, lower than that of Japan, and approximately comparable to that of the United Kingdom (Fig. 1). The main reason could be the use of different pitch among scanners in head examinations. In our study the head was scanned with a pitch between 0.76 and 1.5. In a further finding, the 75th percentile of DLP in head CT examinations was lower than that of Japan and Egypt, whereas it was slightly higher than that of the United Kingdom (Fig. 2). These variations could be due to the difference in the slice thicknesses used by radiology centers, the frequent use of 120 KV or 140 KV tube voltages, and the difference in the scanned volume length in head CT examinations.
Regarding the findings of the DRLs for CTDIvol of the chest and abdomen examinations were significantly lower than those of the studies from Egypt, Japan and the United Kingdom, except that the DRL of the chest examinations was almost similar to the study from the United Kingdom (Figs. 3 and 4). This discrepancy may be due to the CT scanning parameter settings of different scanner manufacturers. Furthermore, significant differences were observed in the DRLs values of DLP for the chest and abdomen CT examinations compared with the other DLPs. The DRL of the chest CT examination in our study was higher than those of all selected studies (United Kingdom, Japan, and Egypt) (Fig. 5). However, the abdomen DRL was significantly lower than those of all the selected studies (Fig. 6). This is due to the absence of local DRLs on which radiology technicians can refer for practice evaluation, variations in the protocols used that were not optimized and techniques of scanned regions. Moreover, the patient weight was not available, thus not allowing to evaluate the body size effect on the DRL value.
This study presented several limitations. First, these established DRLs were implemented at only four Moroccan hospitals and included data from only three CT examinations. Future studies could include other body examinations, pediatric patients and expanding the number of hospitals involved. Second, the CT protocols used were from only four scanner models, given that there are several brands and models of CT scanners installed in Morocco. Third, all the scanners involved in this study had just 16-slice. Moreover, the number of sequences per exam was not available, although this parameter may influence the total DPL value. Finally, difficulty in traveling from hospital to another for data collection, because it is necessary to collect on site important information about the patients who underwent CT scans, such as age. However, this study is important in establishing DRL values available to nuclear medicine staff for protocol optimization purposes.
Local DRLs for CT examinations in Morocco, compared to other DRLs.
Distribution of CTDIvol values for head.
Distribution of DLP values for head.
Distribution of CTDIvol values for chest.
Distribution of CTDIvol values for abdomen.
Distribution of DLP values for chest.
Distribution of DLP values for abdomen.
The purpose of this study was to evaluate the radiation doses of adult patients who underwent three CT examinations including the head, chest and abdomen. The established DRLs of each examination have been compared with those of the United Kingdom, Japan and Egypt. These comparisons have identified high average doses for chest examination. Therefore, it is necessary to implement dose optimization of the collected examination protocols while keeping a good image quality for a reliable diagnosis. This optimization of CT protocols can be achieved by providing correct training to CT staff on factors that affect patient dose and image quality. It is thus essential that the Moroccan agency for nuclear and radiological safety and security (AMSSNuR) should establish in the future national DRLs.
The authors declare that they have no conflicts of interest in relation to this article.
There was no funding from any source for this study.
This study did not carry out activities that would require approval by a research ethics committee.
This article does not contain any studies involving human subjects.
M. El Mansouri and A. Choukri equally contributed as the main contributors of this paper. M. Talbi, O. Nhila and M. Aabid contributed to the collection of data. All authors read and approved the final version of the paper.
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Cite this article as: El Mansouri M, Talbi M, Choukri A, Nhila O, Aabid M. 2022. Establishing local diagnostic reference levels for adult computed tomography in Morocco. Radioprotection 57(1): 61–66
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