Research On The Thyroid Protection Methods During Chest CT Scanning

With the increase of width of detector,the function of computed tomography(CT)gradually expands.The CT examination is more frequently than before.Meanwhile,radiation dose exposed to patients also rises.Scatter dose created by X-ray tube,scanning table,surrounding walls and objects as well as human tissues increases significantly.Therefore,the protection of sensitive organs outside of the scanning area attracts much more attention recently.We investigated CT examination data at First Affiliated Hospital of PLA General Hospital from October 2014 to October 2017.The analysis results showed that chest CT scan is the most frequent examination.Then,we used optically stimulated luminescence dosimeters to measure surface absorbed dose of lens,thyroids and gonads in 100 patients during chest CT scanning.The absorbed dose of thyroid is the strongest among the three sensitive organs.Therefore,this study focuses on the protection of thyroid during chest CT scanning.Based on the research before,a model of variation of absorbed dose with lead equivalent was established in this study.We used different lead equivalent collar to protect the thyroid of phantom during chest CT scan while measuring surface dose of thyroid.According to the surface dose of phantom thyroid,we calculated the coefficients of the model.And the reliability of the model was also verified.The testing results showed that the optimal lead equivalent of thyroid collar was 0.75 mm.In this thesis,body mass index(BMI)was used to separate the different kinds of patients.The radiation dose at the thyroid of patients with different BMI was measured.According to detecting results,we optimized the coefficients of the model and verified the applicability and shielding effect of the protecting collar.It was verified that the protecting collar with0.75 mm lead equivalent could realize the similar effect for the thin,normal,overweight and obese patients.The surface dose at thyroid for the four kinds of patients was decreased by83.5%,91.7%,92.3%,and 92.8% respectively.These data proved that the protecting collar is effective for reducing radiation dose.It can achieve good protective effects for all kinds of patients.The conclusion could give some guidance for the patients to take appropriate protective methods for thyroid during chest CT scanning.