CT검사시 목적장기 이외 부위의 차폐를 통한 피폭선량감소 효과에 관한 연구

Dose Reduction Effect with Shielding of Superficial Radiosensitive Organs of Out-plane in CT Examination

Purpose The study was done to evaluate radiation dose reduction effect through shielding like scattering ray to superficial radiosensitive organs which are adjacent to scanning field when head & neck, chest & abdomen CT examination. Materials and methods LightSpeed VCT(General Electric medical system, Milwaukee, USA) was used as CT equipment and Rando phantom(model RAN-110, Churchin associate LTD., USA) and glass dosimetry system(GD-351, 8.5mm, FGD-1000) in the measurement of radiation dose. There were two kinds of materials to shield from radiation, a lead apron(0.5mm Pb at 80kVp) was used in out-plane and bismuth(F & L medical products co.) was used in in-plane. The measurement of organs was divided into brain, neck, chest and abdomen. Scan protocol was as follow: 1. In the brain examination, 120kVp and dose modulation(1sec, min. 150~max. 250mA, noise index: 2.80) was used for the examination. The glass dosimetry elements were put on left and right lens of phantom eyeball(thyroid), and the radiation dose without and with the use bismuth(Pb) shield were measured three times. 2. In the neck examination, 120kVp and dose modulation(0.6sec, min. 150~max. 300mA, noise index: 6.0) was used for the examination. The glass dosimetry elements were put on left and right lens of phantom eyeball(the both nipples), and the radiation dose without and with the use bismuth(Pb) shield were measured three times. 3. In the chest examination, 120kVp, dose modulation(0.6sec, min. 100~max. 230mA, noise index: 15.86) was used of the pre-contrast and 120kVp, dose modulation(0.6sec, min. 100~max. 275mA, noise index: 15.86) was used of the post-contrast. The glass dosimetry elements were put on left and right phantom thyroid(umbilicus), and the radiation dose without and with the use bismuth(Pb) shield were measured three times. 4. In the abdomen examination, 120kVp and dose modulation(0.6sec, min. 100~max. 300mA, noise index: 11.57) used for examination. The glass dosimetry elements were put on the both nipples of phantom breast(gonad), and the radiation dose without and with bismuth shield were measured three times. Results 1. In brain CT scanning, shielding with bismuth of lens of eyeballs decreased the radiation dose about 46%(without: 43.98mGy, with: 23.86mGy) and shielding with Pb of thyroid decreased the radiation dose about 24%(without: 1.21mGy, with: 0.92mGy). 2. In neck CT scanning, shielding with bismuth of lens of eyeballs decreased the radiation dose about 42%(without: 66.47mGy, with: 38.58mGy) and shielding with Pb of breast decreased the radiation dose about 65%(without: 2.43mGy, with: 0.86mGy). 3. In chest CT scanning, shielding with bismuth of thyroid decreased the radiation dose about 22%(without: 20.74mGy, with: 16.1mGy) and shielding with Pb of umbilicus decreased the radiation dose about 44%(without: 1.34mGy, with: 0.75mGy). 4. In abdomen CT scanning, shielding with bismuth of breast decreased the radiation dose about 13%(without: 1.80mGy, with: 1.58mGy) and shielding with bismuth of gonad decreased the radiation dose about 33%(without: 23.08mGy, with: 15.46mGy). Conclusion According to the study, a percentage of the measured dose reduction is from min. 22% to max. 65%. The results have important meaning that there is much possibility of additional dose reduction through shielding not only in-plane but also out-plane. Consequently, the radiation dose given to patients can be decreased through the CT workers’ effort and concern like shielding out-plane from radiation.