Radioprotection No 59-1 | Page 22

16 M . EL Fahssi et al .: Radioprotection 2024 , 59 ( 1 ), 13 – 18 Table 5 . Comparison of DRLs assessed in terms of CTDI vol and DLP with those of previous studies .

IRSN 2023

Calculated DRLs in terms of CTDIvol and DLP are indicated for each CT-exam . Cþ : with contrast media . C� : without contrast media .

Table 6 . p-value distribution according to the relationship between sex , age , body mass index and effective dose for each examination .

Brain C�

Chest C�

Effective dose ( p-value )

Abdomen Cþ

Abdomen C�

** Correlation is significant if p-value < 0.05 .

AP Cþ

CAP Cþ

The charge is also fixed at 120 mAs for all CT-exams except Chest CT without contrast media . This situation is due to the use of standard protocols , and the lack of adjustment of these protocols to the patient ’ s morphology . In fact , lowering the tube voltage to achieve dose reduction has been proposed . However , it should be accompanied by an image quality measurement to verify that no diagnostic information will be lost ( Christos P et al ., 2022 ). For the iodine contrast , there is a strong dependence on tube potential , which is much in favour of lower kV settings . Therefore , 80 instead of 120 kV would allow the patient dose to be reduced by almost a factor of two without sacrifying image quality ( Nagel , 2007 ). Usually , the average voltage and charge used for the head region are higher than those used for the AP and CAP regions . This leads to lower DRLs in terms of CTDIvol , and consequently , DLP for the AP and CAP regions ( Hasan et al ., 2022 ). Consequently , the fixed value of these technical parameters ( kV and mAs ) used in this study will have an effect on the comparison of the dosimetric data collected with those from similar studies .

In terms of effective dose , the results show that the average effective dose calculated for CT scans of the brain without contrast media ( 2.37 mSv ) is higher than that indicated by the International Commission on Radiological Protection Publication No . 103 ( 1,7 mSv ) ( ICRP , 2007 ). The effective doses calculated by this study for the chest without contrast media , AP with contrast media and CAP with contrast media were 6,50 , 5,07 , and 7,13 mSv respectively . These values are all lower than those indicated by ICRP Publication 103 which are 6,8 , 15,5 , and 18,3 mSv respectively .

DRLs in terms of CTDI vol , and DLP for brain without contrast media are 64,45 mGy , and 1405,77 mGy . cm respectively . These values are higher than those reported by two Moroccan surveys ( Semghouli et al ., 2022a ( CTDI vol : 40,94 mGy ; DLP : 969,90 mGy . cm ) ; El Mansouri et al ., 2022 ( CTDI vol : 57.4 mGy ; DLP : 1020 mGy . cm )), and higher than those fixed by the Institute for Radiological Protection and Nuclear Safety ( IRSN ) ( CTDI vol : 46 mGy ; DLP : 1020 mGy . cm ) ( IRSN , 2023 ), and higher than those reported in Saudi Arabia ( CTDI vol : 48 mGy ; DLP : 962 mGy . cm ) ( Albahiti et al ., 2022 ). Brain CT protocols for this study did not consider patient ’ s gender or the size and shape of the skull , which could influence the dose distribution in CT examinations . In addition , the contribution of overranging to the total CT dose is thus considerably higher for CT examinations with shorter scan ranges such as head CT ( Kayun et al ., 2021 ). These high dosimetric values could also be due to the use of mAs and kVp higher than the international recommended value , the lack of sufficient manpower , and the lack of evidence of quality control checks on the CT machines ( Abdulhamid , 2022 ). In addition , there was no significant relationship between patient gender and effective dose for brain CT examinations ( p = 0.514 ). However , there was a significant relationship between patient age and effective dose ( p = 0.023 ). Age was significantly and negatively associated with the effective dose . In this context , Khursheed et al . found that an inverse trend is observed between normalized effective dose and phantom age for scans of four regions of the trunk and head ( Khursheed et al ., 2002 ). The results show also no association between BMI and the effective dose for brain CT . In fact , for CT imaging of the skull or brain , BMI does not show good accuracy because the effective diameter of the head does not very much in adults ( Steiniger et al ., 2022 ). The higher