두개부와 흉부 CT 검사시 Bismuth 차폐재를 이용한 안구의 렌즈와 유방의 선량감소에 대한 평가

The analysis for the reduction of radiation dose of breast and lens in eyeballs during the CT examination of cranium and chest using Bismuth shields

Purpose Bismuth shield can filter twice in that penetrates X-ray, which is essential in diagnosis, and it also partially decreases skin dose. Hence, it is necessary to study the effects in reduction of absorbed dose on highly sensitive organs, which are included in the regions of cranial and chest CT exams. Materials and methods All exams were proceeded on LlghtSpeed 16MDCT (GE Medical System, Milwaukee, U.S.A.), Rando phantom (Model RAN-110, Churchin associate LID., USA) and Glass dosimetry system(GD-351,8.5mm, FGD-1000) for the measurement of radiation dose. In addition, AttenuRad radiation protection devices of eyeballs & breast (F&L Medical Products Co.) are used for protection of sensitive organs. In cranial examination, the brain CT protocols was used for the examinations, and the summary of it is as followed: The glass radiation elements were put on left and right lens of phantom eyeballs, and the radiation before and after the use of Bismuth shield were measured twice when 120kVp of current were changed into 150mAs, 200mAs, and 200mAs, and when 250mAs were changed into 100kVp, 120kVp, and 140kVp. In chest examination, low-dose protocol and chest routine protocol are used for the examination. The conditions of low-dose protocol are as followed:120kVp, noise index 11.57(10~50mA), tube rotation time 0.8sec, pitch 1.375, and table speed 13.75mm/sec. Also, the conditions of chest routine CT protocol are 120kVp, noise index 15.86(160~250mA), tube rotation time 0.8sec, pitch 1.35, and table speed 13.5mm/sec. The glass elements were put on the both nipples of phantom and the radiation before and after the use of bismuth shield were measured twice. When the shield is used, rubber-made spacer(1cm) should be on the breasts, followed by bismuth shield, because it decreases not only the scattering ray absorption into breast wall caused by bismuth shield but image artifact potentially. Results The result of the measurement of orbit shielding during cranial examination. The results of measurements of the radiation(from 120kVp to 150, 200, 250 and 300mAs) before and after the use of bismuth shield are as followed: from 18.4±0.3mGy to 10.25±0.5rnGy(44.3% decrease) at 150mAs; from 23.9±0.9mGy to 13.9±0.1mGy(41.5% decrease) at 200mAs; from 37.3±0.3mGy to 19.8±0.9mGy(47.1% decrease) at 250mAs; and from 47.8±3.4mGy to 24.4±1.4mGy(46.8% decrease) at 300mAs. On the other hand, the measurements of radiation(from 250mAs to 100, 120, and 140 kVp) before and after the use of bismuth shield are as followed: from 22.9±0.2mGy to 22.9±0.2mGy(51.2% decrease) at 100kVp; from 34.4±0.9mGy to 19.5±0.2mGy(43.3% decrease) at 120kVp; and from 49.5 ±4.4mGy to 29±1.2mGy(41.4% decrease) at 140kVp. The result of the measurement of orbit shielding during breast examination. In low-dose protocol, the results of measurements of the radiation before and after the use of bismuth shield are 3.16±0.02mGy and 2.44±0.03mGy(22.78% decrease), respectively, and in chest routine protocol, the results were 14.45±1.08mGy and 11.93±0.21mGy(17.43% decrease), respectively. Conclusion In cranial examination, there was not much change in the radiation dose of eye lens with an application of bismuth shield, even increases of mAs with constant kVp. On the other hand, the rate of reduction of radiation dose by bismuth shield is seen with constant mAs and increase of kVp. Due to the use of bismuth shield, radiation dose has been decreased about 22.8%in low-dose study, and 17.4% in chest routine study. In our hospital, the use of bismuth shield of orbit is not applied to adults, but applied to some infants only when brain CT exam was operated to them. The breast shield is applied, as a test, to women under 50 years old. According to this study, the results show obviously that the use of the bismuth shield can reduce radiation dose of highly radiation-sensitive organs. As mentioned before, the amount of radiation that eye balls received at 250mAs(at