Radiation doses during computed tomography scan imaging in Hassan II Hospital, Agadir, Morocco

Introduction the aim of this study was to establish local Diagnostic Reference Levels (DRLs) for four adult Computed Tomography (CT) examinations in the radiology department, Hassan II hospital of Agadir. Methods during this survey, we have examined the data of 200 patients at an average of 50 per localization. A General Electric 16 CT with automatic exposure control system was used to perform all CT examinations. Scanner acquisition parameters, number of series, contrast medium use, rotation time plus slice thickness, the displayed Computed Tomography Dose Index (CTDIvol), and the Dose Length Product (DLP) were among the data collected for each diagnostic exam chosen. To evaluate the DRL and effective dose, the conversion factor and formalism of the International Commission on Radiological Protection (ICRP) were utilized. Results the average effective dose (Eeff), the displayed CT dose index (CTDIvol), dose length product (DLP) were (7.28±2.35) mSv, (10.80±3.80) mGy and (428.35±138.26) mGy.cm respectively at chest CT. For abdomen-pelvis CT scan, there were (12.48±5.58) mSv, (9.30±2.99) mGy and (805.43±359.98) mGy. Those at chest abdomen-pelvic CT scan were (11.72±3.98) mSv, (10.82±2.53) mGy and (755.97±251.52) mGy.cm respectively. For lumbar CT, there were (12.12±2.32) mSv, (26.46±5.24) mGy and (787.00±149.37) mGy.cm respectively. Conclusion the findings of this study shows that our values are slightly higher than those of developed countries. This first-ever CT practice evaluation at Agadir's Hassan II Hospital reinforced the need for further radiology training for computed tomography practitioners on parameters influencing image quality, dose, and protocols improvement.


Introduction
The International Commission on Radiological Protection (ICRP) defines the principles of radiation protection as being the justification, optimization, and dose limitation [1]. The dose limitation principle does not apply to medical exposures to preserve the potential benefit of exposure; instead, the ICRP defines Diagnostic Reference Levels (DRLs) as a value to compare practices [2]. Thus, the International Basic Safety Standards (also known as BSS) require the establishment of DRLs to indicate the necessity for an inquiry to determine whether the values in practice are excessively high or unexpectedly low [3]. Such DRLs should be founded, as much as possible, on large-scale surveys that are relevant to the local circumstances. Moroccan radiological legislation lacks these requirements. Despite the need and widespread attention on this topic, research on large-scale nationwide surveys of patients during medical radiation exposure for assessing DRLs is primarily from Europe [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The Computed Tomography (CT) scans are a relatively high-dose imaging procedure that is known to contribute significantly to individual and community doses [18,19]. Therefore, the actions for practice and optimizing radiation protection of patients should be prioritized and implemented for the CT modality.
Despite the growing number of CT machines in Morocco, the Diagnostic Reference Levels (DRL) have yet to be defined. Thus, several previous studies have shown a significant variation in the doses administered to patients for the same radiological examination procedure [20][21][22][23][24][25][26]. The aim of this pilot study at Hassan II Hospital of Agadir was to estimate the doses during radiation medical exposure of four CT scan procedures so that local diagnostic reference levels (DRLs) could be established.

Methods
A descriptive study in medical imaging was conducted at Hassan II Hospital in Agadir from September 2019 to January 2020. A general electric 16 CT with automatic exposure control system was used for all CT exams. The machine's quality controls were checked regularly, and all of the measurement parameters were within acceptable limits.
In this survey, 200 patients were considered for four CT imaging procedures, with 50 patients per localization. Patient-related parameters (age, clinical data, contrast media use), as well as X-ray exposure parameters, were collected. Other exposure-related parameters such as gantry tilt, tube current (mA), exposure time, tension (kV), slice thickness, number of slices, table increment, and the dose length product DLP (mGy.cm), as well as started and finished locations on the displayed CT dose index CTDI vol (mGy), were taken into account. The International Commission on Radiological Protection (ICRP) conversion factor was used to evaluate the effective dose and DRL [9].

Statistical analysis: it was conducted by Microsoft
Office Excel 2007. The arithmetic mean (also denoted as mean) and third quartile (75 th percentile) are used to express quantitative variables. Descriptive statistics were used to evaluate the CT data. Average CTDI vol (mGy) for each sequence and total DLP per examination were calculated. The typical dose was estimated using median DLP and CTDI vol (mGy) data. The rounded third quartile values of median distributions for CTDI vol (mGy) and DLP (mGy.cm) data were used to set the DRL for Hassan II Hospital in Agadir. The results obtained were compared with those established by other countries.

Results
Of the 200 CT scans collected, 25% were for the chest, 25% for the abdomino-pelvic, 25% for the chest-abdomen-pelvis, and 25% for the lumbar spine. The patients' average age was (48 ± 17) years (20-90 years), with 60% of them being 45 years old. The chosen patients' average weight was (67 ± 8) kg. All protocols were helical and had a voltage of 120 kV for the Acquisition parameters of the four procedures. With extremely varied acquisition parameters, the maximum charge (mAs) was used for chest abdomino pelvic and lumbar spine CT scans (350 mAs average) ( Table 1).

Patient-doses for four commonest CT-exams:
the results obtained show a variation in patient doses for the four most common CT examinations studied. The lumbar spine CT scan (mean 651 mGy.cm) showed the smallest dose variation (2fold) while the greatest patient-dose variability was observed in the abdominal pelvic CT scan (8-fold) ( Table 2).
Comparison of DRLs obtained in this study with those adopted by other countries: in Agadir's Hassan II hospital's radiology department, we were able to establish DRLs for chest, abdomino-pelvic, chest abdomino-pelvic, and lumbar spine CT-scans for adults depending on the 75 th percentile of the DLPs distribution in our sample (Table 3).

Discussion
This descriptive study was carried out to propose DRLs for four of the most common adult CT-scan examinations at the radiology department of Hassan II hospital in Agadir. The 75 th percentile of DLP was 428 mGy.cm, 756 mGy.cm, 805 mGy.cm, and 787 mGy.cm for chest, chest abdomen pelvic, abdomino-pelvic, and lumbar spine CT-scans, respectively. Apart from the thoracic abdominopelvic procedure, our DRL values are superior to those established by other countries such as the United Kingdom (2014), France (2016), China (2019), and Belgium (2020) [4,[27][28][29]. Furthermore, our DRLs for chest CT-scan, are lower than those in Cameroon (2017) [30]. Consequently, our patientdoses DRLs are between those of industrialized countries with advanced facilities and advanced cultures of optimization, such as China, the United Kingdom, France, and Belgium, and DRLs of an African country such as Cameroon. Looking forward to the development of a program to establish diagnostic reference levels at the national level, the DRLs obtained in this study can be used for optimization in Agadir's Hassan II Hospital. Radiologists should methodically add DLP notification on radiological reports for patient radioprotection reasons [31]. On lumbar spine CT scans, higher DRLs have been seen in Belgium, China, the United Kingdom, France, and Cameroon [4,[27][28][29][30]; this is due to the presence of multiple high attenuating bone structures in the spine, which necessitates the use of large doses to provide satisfactory image quality. We have evaluated the first results of DRLs, which can already be used for optimization while we wait for a national survey to assess the DRLs with the help of competent authorities. In Morocco, further research is needed to establish DRLs for pediatric CT as well as for procedures of all radiological modalities.

Conclusion
The results obtained show that DLP values of 428 mGycm, 756 mGy.cm, 805 mGy.cm, and 787 mGy.cm for chest, chest abdomen pelvic, abdomino-pelvic, and lumbar spine CT-scans, respectively, can be utilized as diagnostic reference levels in CT imaging in adults in Agadir's Hassan II hospital's radiology department. These DRLs are slightly higher than those of some developed countries. Hence the need for a periodic continuous training program on the parameters influencing the quality of the images, the dose, and the improvement of the protocols for the practitioners.

What is known about this topic
 Computed tomography scan exposures data are not yet investigated at this center;  The radiation doses for CT scan procedures are not yet documented;  Diagnostic reference levels data are not yet established for CT scan procedures.
What this study adds  The DRLs established will guide the process of optimization;  The variations in the radiation dose during CT scan practice will be limited;  This is the first assessment of DRLs in our radiology department.

Competing interests
The authors declare no competing interests.

Authors' contributions
SS is involved in study conception, data analysis, interpretation of the data, and manuscript writing. BA and SW are involved in the data interpretation and critical review of t manuscript. All the authors have read and agreed to the final manuscript. Table 1: average acquisition parameters of the four most common CT-scan imaging in our service Table 2: mean dosimetric parameters CTDI vol , DLP, and their ranges per localization studied