Radioprotection No 59-4 | Page 42

F . Poursoltani et al .: Radioprotection 2024 , 59 ( 4 ), 278 – 286 281 Fig . 2 . CTDI phantom ( a ), five ROIs in the CTDI phantom image to evaluate noise and CT number in images ( b ).

Table 1 . Measured mean breast surface dose during thoracic CT scans with and without the constructed shields .

Dose reduction (%) = 100 [( Measured dose without shield � Measured dose in presents of shield )/ Measured dose without shield ]. pixels inside the ROIs were considered as the average CT number and their standard deviation was considered as the noise . The mean CT number and standard deviation within each ROI were averaged for seven consecutive images . CT numbers shift and image noise increase percentage with and without shields are also shown in Figure 3 . The shield with 50 % Cu – 50 % BaSO 4 had the lowest destructive effect on the image quality considering the image noise and CT numbers shift . CT number shift and image noise decrease with increasing distance between shield and ROI in the image . The effect of 50 % Cu – 50 % BaSO 4 shield on the CT number in all regions except the left peripheral region and on the noise in all regions except the anterior and middle regions was not statistically significant ( p > 0.05 ).

0.05 . Furthermore , the Shapiro – Wilk test was used for assessing the normality of the data . All data had a normal distribution .

3 Results

3.1 Breast surface dose on the human thorax phantom

Mean values entrance skin dose ( ESD ) and percentage of dose reduction in CT imaging without and with radiation shields are listed in Table 1 . Using on phantom TLD measurements , the average breast surface dose without radiation shield was 15.03 mGy . The surface dose was reduced ( compared to without radiation shield ) by 14.17 % to 51.69 % with the use of radiation shields . The p-values ( for comparison of groups with shield compared to the group without shield ) of all radiation shields except 100 % BaSO 4 shield were statistically significant ( p < 0.05 ).

3.2 Image quality using CTDI phantom

Shields were placed on the CTDI phantom during CT scanning to assess the image quality . Five desirable circular areas ( ROIs ) were considered in the phantom image with different distances from the shield . The mean values of the

3.3 Image quality analysis by patient study

For the patient study , 50 % Cu – 50 % BaSO 4 shield was chosen due to its less impact on image quality . An axial chest CT image of a patient using a 50 % Cu – 50 % BaSO 4 shield is shown in Figure 4 . Based on the results of the radiologist ’ s evaluation ( Tab . 2 ), no artifact was observed in the 30 patients of the intervention group . In the case of image quality , there was no significant difference between the intervention and control groups . The radiologists declared that all CT images were had p-value of normal diagnostic quality .

4 Discussion

The use of CT and its associated radiation dose has been increased in recent years ( Bertho et al ., 2024 ). In the recent years , special attention has been focused on more sensitive organs such as the lens of the eye , thyroid , and breast during CT scanning . Although the breast is not the target of the thorax CT examination , the main drawback of this imaging method is that it exposes the breast to ionizing radiation . In large-scale epidemiological studies ( Mathews et al ., 2013 ; Miglioretti et al ., 2013 ), it has been shown that the risk of developing cancer in children and young adults is increased due to radiation exposure after CT examinations . Studies on women