106 J. Bazoma et al.: Radioprotection 2026, 61( 2), 105 – 112
mGy) and the dose-length product( DLP in mGy. cm)( ICRP, 2017). Diagnostic Reference Levels( DRLs) are usually proposed in terms CTDI vol and DLP. These two quantities are based on standard-size cylindrical phantoms( 16-and 32 cm phantoms) and do not take into account patient size apart from the patient scan length which is incorporated in DLP computation. Size-Specific Dose Estimates( SSDE) were developed to address this issue( AAPM, 2011). However, SSDE are not appropriate to estimate organ doses( Boone, 2012; Sahbaee, 2014). Yet, the determination of organ doses( D T, in mGy) is capital as they are required for assessing the probability of cancer induction in exposed individuals( ICRP, 2007). Finally, the effective dose( E, in mSv) is a quantity mainly used to compare radiation doses from different diagnostic procedures and for comparing the use of similar technologies and procedures in different hospitals and countries as well as the use of different technologies for the same medical examination( ICRP, 2007).
At the national level, studies on organ dose estimation( Bazoma, 2022) and on establishment of typical dose reference level values( Dallou, 2024) have been conducted. These studies have shown that, in some cases, the doses delivered to the organs of patients undergoing CT examinations were very high, hence the need to conduct this study based on new equipment with current technology.
The objective of this study was to assess typical( DRL) values, SSDE, organ doses and effective doses of adult patients undergoing CT examinations in a university hospital in Brazzaville, Congo Republic.
2 Material and methods
2.1 Material
This study was carried out using a CT machine of the brand CT Canon( serial number: 4AA2233376) of 80 slices, installed in the service of medical imaging of the university hospital of Brazzaville in the Republic of Congo. The frequency of CT scan examinations is up to 50 patients per week. This CT machine was manufactured in March 2022 and put into service in July 2022.
2.2 Methods 2.2.1 Collection of data
This study is a retrospective study that involved 308 adult patients. The data were manually collected from the console of the CT machine used. The data were collected from September to December 2023. The institutional review boards of the university hospital judged that this research work did not need to obtain patient informed consent. All patient data were anonymized before their evaluation. All data were handled in agreements with the research authorization No. 0378 / MSP- CAB / DGAR / DARH / SFS-24 granted by the Ministry of health and population, Republic of Congo, and the research authorization No. 044 / MSP / CHUB-DG / DERE / SR-23 granted by the General Directorate of the university hospital of Brazzaville. The information collected was the following: the examination type( head, chest, abdomen-pelvis � AP, chestabdomen-pelvis � CAP CT scans), age and sex of the patients, the anteroposterior( AP) and lateral( LAT) dimensions of patients, and the machine parameters( kV, mAs, CTDI vol, DLP, pitch, slice thickness, collimation, field of view) associated with the examination.
2.2.2 Statistical analysis
The data collected in this study were analyzed using the softwares Microsoft Office Excel Professional Plus 2013( Microsoft corporation, USA) and Matlab( The MathWorks, Inc, USA), version R2013a. They were mainly used to plot graphs and compute statistical parameters such as the mean values, standard deviations, quartiles, etc.
2.2.3 Typical values
Since only one CT facility was involved in the present study, the median values of the distribution of DLP and CTDI vol of the head, chest, AP and CAP CT examinations were defined as typical( DRL) values in agreement with the ICRP publication 135( ICRP, 2017).
2.2.4 Size-specific dose estimates
SSDE were calculated( AAPM, 2011):
SSDE ¼ f 32D size
using the following formula
CTDI32 vol;
for the 32 cm diameter reference phantom, used for body examination of adult patients. The superscript D corresponds to the conversion factor f 32 size related to effective diameter given in Table 1D of the reference( AAPM, 2011). The effective diameter D eff was calculated through the following formula: p D ef f ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
AP LAT: ð2Þ
2.2.5 Organ and effective doses ð1Þ
A Monte Carlo-based method was used to compute organ and effective doses. Dose coefficients for adult patients were used to convert CTDI vol to organ doses using the following formula( Bazoma, 2022; Lee, 2015):
D T ¼ CTDI vol DC; ð3Þ
where D T is the dose to the organ or tissue T and DC( in mGy / mGy) is the CTDI vol �normalized organ absorbed dose coefficient which is a function of the organ of interest, the patient sex, age and size, and the scanner beam quality. DCs used in this study were for 35 years-old adult male and female ICRP reference phantoms. DCs values less than 0.02 mGy / mGy were not provided in the tables and were attributed a value of 0 mGy / mGy in the present work.
Effective doses were computed using the calculated organ dose values and tissue weighting factors given in ICRP publication 103( ICRP, 2007) according to the following equation:
E ¼ X
H M T
W þ HF T T; ð4Þ 2
T