280 F . Poursoltani et al .: Radioprotection 2024 , 59 ( 4 ), 278 – 286
form of cubes with dimensions of 2.3 2.3 0.9 mm 3 ). In order to read TLD dosimeters , a KFKI RMKI-TLD Reader ( KFKI Research Institute of the Hungarian Academy of Sciences , Budapest , Hungary ) was used . Dose measurements were carried out with and without the shields , separately . Each measurement was repeated for three times . To measure the dose with and without the shields using the TLD dosimeters , three TLDs were placed on the right breast and three TLDs on the left breast ( Fig . 1c ). The average of these measurements was considered as the absorbed dose of both breasts .
2.4
Image quality assessment
The image quality without and with the shields was quantitatively evaluated using a CTDI acrylic homogenous phantom ( Fig . 2a ), which is a cylindrical phantom with diameter of 24 cm and length of 15 cm by measuring the image noise and CT numbers shift in different regions of interests ( ROIs ). Image noise was evaluated using the standard deviation of the attenuation values ( in HU units ) in the homogeneous region . In the phantom image , a 2 cm 2 region of interest ( ROI ) was considered in the center of the phantom and four ROIs in the adjacent parts ( Fig . 2b ). The mean CT number and standard deviation within each ROI were calculated in seven successive axial images and then averaged .
2.5 Patient study
Fig . 1 . Radiation shield ( a ), thorax phantom and breast phantom ( b ), thorax phantom and breast phantom with the shield and dosimetry instrument ( c ).
using a humanoid thorax phantom and breast phantom ( Fig . 1b ). The phantom used in this study was made of materials with electron density similar to real human chest structures , including cork with CT numbers in the range of 774 – 841 Hounsfield Unit ( HUs ) representing the lungs , plexiglas with 80 – 171 HUs as the soft tissue and finally a dense fiber ( phenolic resin cotton fiber rod ) with 565 – 717 HUs instead of vertebral bones . It is worth mentioning that the spectrum of HUs presented above was obtained from the treatment planning system ( TPS ) software ( Ehtiati et al ., 2021 ). The diameter of the breast phantom was 160 mm and its height was 80 mm . The breast phantom was made using silicone materials and a 2 % catalyst was added to improve the process and quality of the breast phantom . The breast phantom was placed on the thorax phantom to resemble the actual position of the breast on the chest wall . Based on human anatomy , the breast was located between the second and sixth or seventh ribs ( in the vertical dimensions ). The surface breast radiation dose was measured with Harshaw TLD-700 ( Harshaw USA ) dosimeters ( LiF : Mg , Ti , in the
For image quality assessment , a controlled trial with a parallel group design was conducted . All procedures were in accordance with the ethical standards of ethics committee of Semnan university of Medical Science , Iran . 60 female patients were recruited in this study and divided into two equal intervention and control groups . The Important point is that imaging was parts of the patient ’ s diagnostic processes and no additional radiation was given to the patients . The criteria for patients to enter the study were female patients aged 20 – 75 who underwent thoracic CT examinations , and the criteria for patients to leave the study were patients who had a reduced level of consciousness ( as a result of trauma , stroke , or other factors ) or the patient ’ s lack of consent to continue participating in the research .
In the CT scan department , after filling informed consent forms by the patients , the optimized shield was placed over the breast organ after the scout scan in the intervention group . In the control group , the patients underwent routine CT imaging of thorax without radiation shield on the breast organ . Before assessing the CT images , image of the shield was removed from the images of the intervention group , and then the images of the intervention and control groups were given to two radiologists . A checklist form was filled about the absence or presence of artifacts ( Streak or beam hardening artifact ) in the breast , mediastinum , and lung parenchyma regions .
2.6 Statistical analysis
The difference between different groups ( the group with different shields and the group without shield ) was evaluated using paired t-test . Statistical significance was set at p-value less than