Radioprotection No 59-2 | Page 65

124 S . Semghouli et al .: Radioprotection 2024 , 59 ( 2 ), 123 – 130
attributed to a lack of optimisation of radiographic protocols for CT , although it may also be due to the poor condition of the equipment ( IAEA , 2012 ). Overall , CT plays a crucial role in estimating the collective effective dose from diagnostic imaging worldwide , which is approximately 4 million person-Sv / year ( AAPM , 2008 ). In addition , approximately 2 % of all cancer cases in the United States can be attributed to CT and fluoroscopy ( Shyu , 2016 ).
The optimization of various parameters can be employed to decrease the amount of radiation exposure experienced by patients during CT scans . These parameters include tube current , tube potential , patient positioning , scan range , reconstructed slice thickness , and pitch , as noted by Raman et al . ( 2013 ). The INWORKS study shows an increase in the relative rate of mortality from solid cancers with increasing cumulative exposure to ionizing radiation at low doses to which nuclear workers are generally exposed in France , the United Kingdom , and the United States ( Richardson et al ., 2023 ). The use of CT scans for radiotherapy planning differs from diagnostic CT scans in terms of technique , radiation dose , and associated risk . Sanderud et al . ( 2016 ) demonstrated that the absorbed radiation dose is significantly higher for radiotherapy planning CT scans than for diagnostic CT scans of the thorax . One of the fundamental principles in optimizing protection against medical exposure is the implementation of diagnostic reference levels ( DRLs ). DRLs are effective tools for optimizing the protection of patients undergoing diagnostic and interventional procedures . DRLs are not intended for use in radiation therapy . However , they should be considered for imaging purposes in treatment planning , treatment rehearsal , and patient set-up verification in radiotherapy ( ICRP , 2017 ).
In general , DRLs have been established on the basis of the anatomical region explored . However , the current trend is toward establishing DRLs based on clinical indications . In this context , the ICRP introduced the clinical approach to DRLs several years ago ( Vañó et al ., 2017 ), and many countries have recently implemented DRLs based on clinical indications ( DRLci ), and others are considering doing so soon . Furthermore , the European Society of Radiology ( ESR ) has identified the development of DRLci for both adults and children as one of its key objectives ( Bauhs et al ., 2008 ).
In Morocco and more precisely in the Souss Massa region , we lead a program that aimed at optimizing the doses delivered to patients in medical imaging and improving radiation protection procedures and practices . These studies cover several fields such as optimization in medical imaging ( Amaoui et al ., 2019 , Semghouli et al ., 2022a , Semghouli et al ., 2022b , El Fahssi et al ., 2023a , 2023b , Semghouli et al ., 2023 ), prevention of radiation-induced risks ( Aabid et al ., 2019 ; Semghouli et al ., 2022c ), and practitioners ’ knowledge of patient radiation protection ( Amaoui et al ., 2023 ).
Following on from this work , this study aims to establish diagnostic reference levels and radiation-induced risk for the diagnostic CT-scans and the radiotherapy planning CT-scans of the thorax in the regional hospital of Agadir , Morocco .
2 Materials and methods
2.1 Populations studied
Data from two groups of patients undergoing thoracic CTscans with either diagnostic CT-scans ( G1 , n = 120 ) or Radiotherapy planning CT-scans ( G2 , n = 120 ) were collected between January and March 2023 .
For diagnostic CT scans , three clinical indications were selected : pulmonary embolism , infectious lung disease and chronic obstructive pulmonary disease ( COPD ), with 40 CT examinations per indication .
Our data are collected from two types of scanners , Optima General Electric 16-slice for diagnostic CT-scans and Aquilion Lb Canon-Thoshiba16-slice for radiotherapy planning CTscans . The type of acquisition of these two scanners is helical . The scanner acquisition parameters , number of series , use of contrast medium , rotation time in addition to slice thickness , computed tomography dose index ( CTDIvol ), and dose length product ( DLP ) were explicitly delineated for each examination .
2.2 Dose assessment and cancer risk
DRLs were calculated for each type of thoracic CT-scans by estimating the 75 % percentile of the CTDI vol and the DLP . For the effective dose ( E eff ), it is calculated according to the following formula ( Delchambre , 2012 ):
E eff ðmSvÞ ¼ F CD DLP ; ð1Þ
where : F CD is the effective dose conversion factor for CT scan of the Thorax ( ≈0.014 mSv mGy �1 cm �1 ).
The total cancer risk R C is calculated according to the ICRP publication 103 as follow ( ICRP , 2007 ):
R C ¼ E eff ðmSvÞ F cr ; ð2Þ
where E eff is the effective dose in Sv . � F cr = 5.5 10 �2 Sv �1 is the risk coefficient factor .
2.3 Data analysis
The data are statistically analysed by SPSS softwareV21.0 . The student ’ s t-test was used to establish the relationship between gender , clinical indication , and effective dose . The Spearman test was used to establish the relationship between age , BMI , and effective dose .
3 Results
According to Tables 1 and 2 , the population studied was made up of 55 % men and 45 % women for diagnostic CTscans and 40 % men and 60 % women for radiotherapy planning CT scans . The mean age for diagnostic CT scans was 51 years and that for radiotherapy planning CT scans was 52 years . The average BMI for diagnostic CTscans was 24.34 kg / m 2 and that for radiotherapy planning CT scans was 25.71 kg / m 2 . The acquisition parameters for each type of CT scan are presented in Table 3 .