• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3660-3671
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• 2022

A new methodology to derive a dose constraint for radioactive effluent from a unit of nuclear power plant (NPP) through retrospective assessment was developed to reflect operational flexibility in line with international standards. The new dose constraint can retain the safety margin between the offsite dose and the past dose constraints. As case studies, the new approach was applied to 24 Korean NPPs to address the limitations of the existing seven dose constraints that do not fully comply with current international radiation protection standards. Therefore, an effective dose constraint for Korean NPPs was proposed as no less than 0.15 mSv/y, which is comparable to the international practices and previous studies (0.05-0.3 mSv/y). Although the lower bound of the equivalent dose constraint was calculated as 0.17 mSv/y, it is not proposed in this study since the compliance with the derived effective dose constraint can prevent accompanied equivalent doses to any organs from exceeding equivalent dose limits. The new framework and the case studies are expected to contribute toward and support the revision of existing dose constraints for radioactive effluent from NPPs, ensuring better compliance with the current international safety standards as well as reflect the operational flexibility in practice.

• 대한방사선기술학회지:방사선기술과학
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• 제32권3호
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• pp.299-306
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• 2009

MDCT의 시간분해능 향상과 등방성 해상능(isotrophic resolution) 영상의 획득, 그리고 지능적인 심전도 동조를 바탕으로 하여 심혈관 질환의 효과적인 진단검사로 인정받고 있는 후향적 심전도 동조화(retrospective ECG gating) 하의 coronary CT angiography는 상대적으로 많은 환자선량을 제공함으로 인해 우수한 진단방법으로서의 장점을 반감시키고 있다. 이에 각 장치 제조사에서는 환자선량을 감소시키는 방법의 연구가 활성화되어 왔으며, 이의 일환으로 지능적인 cardiac dose modulation 기술과 전향적 심전도 동조화(prospective ECG gating)를 사용한 sequential scan이 도입되고 있다. 이에 본 연구에서는 64 채널 MDCT에서 54 kg, 163 cm인 여성 인체모형팬텀을 대상으로 하고 형광유리선량계를 사용하여 후향적 심전도 동조화 하의 coronary CT angiography 프로토콜에서 환자선량의 정량적 평가와 환자선량 감소를 위해 본원에서 선택적으로 적용하고 있는 5가지 검사 프로토콜을 적용하였을 경우의 effective dose와 중요 부위의 organ dose를 측정 비교하여 다음과 같은 결과를 얻었다. 1) Dose modulation없이 120 kVp와 210 mAs의 노출조건으로 retrospectively ECG gated helical scan으로 시행한 conventional coronary CT angiography 프로토콜의 effective dose는 17.8 mSv였으며, 심장의 organ dose는 103.8 mGy였다. 2) 관전압을 120 kVp에서 100 kVp로 낮추었을 경우 effective dose는 11.0 mSv로 conventional coronary CT에 비해 38.2%가 감소하였으며, 심장은 67.3 mGy로 45.2%가 감소하였다. 3) Cardiac dose modulation을 적용한 경우 effective dose는 13.3 mSv로 conventional coronary CT에 비해 25.3%가 감소하였으며, 심장은 80.0 mGy로 22.9%가 감소하였다. 4) 100 kVp의 저관전압과 cardiac dose modulation을 적용한 경우 effective dose는 8.1 mSv로 conventional coronary CT angiography에 비해 54.5%가 감소하였으며, 심장은 49.5 mGy로 52.3%가 감소하였다.

• Journal of Radiation Protection and Research
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• 제46권4호
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• pp.151-159
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• 2021

Background: Computed tomography (CT) is one of the crucial diagnostic tools in modern medicine. However, careful monitoring of radiation dose for CT patients is essential since the procedure involves ionizing radiation, a known carcinogen. Materials and Methods: The most desirable CT dose descriptor for risk analysis is the organ absorbed dose. A variety of CT organ dose calculators currently available were reviewed in this article. Results and Discussion: Key common elements included in CT dose calculators were discussed and compared, such as computational human phantoms, CT scanner models, organ dose database, effective dose calculation methods, tube current modulation modeling, and user interface platforms. Conclusion: It is envisioned that more research needs to be conducted to more accurately map CT coverage on computational human phantoms, to automatically segment organs and tissues for patient-specific dose calculations, and to accurately estimate radiation dose in the cone beam computed tomography process during image-guided radiation therapy.

• Journal of Radiation Protection and Research
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• 제36권4호
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• pp.183-189
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• 2011

To quantitatively evaluate how setup errors in conjunction with dose gradients contribute to the error in IMRT dose quality assurance (DQA) measurements. The control group consisted of 5 DQA plans of which all individual field dose differences were less than ${\pm}5%$. On the contrary, the examination group was composed of 16 DQA plans where any individual field dose difference was larger than ${\pm}10%$ even though their total dose differences were less than ${\pm}5%$. The difference in 3D dose gradients between the two groups was estimated in a cube of $6{\times}6{\times}6\;mm^3$ centered at the verification point. Under the assumption that setup errors existed during the DQA measurements of the examination group, a three dimensional offset point inside the cube was sought out, where the individual field dose difference was minimized. The average dose gradients of the control group along the x, y, and z axes were 0.21, 0.20, and 0.15 $cGy{\cdot}mm^{-1}$, respectively, while those of the examination group were 0.64, 0.48, and 0.28 $cGy{\cdot}mm^{-1}$, respectively. All 16 plans of the examination group had their own 3D offset points in the cube. The individual field dose differences recalculated at the offset points were mostly diminished and thus the average values of total and individual field dose differences were reduced from 3.1% to 2.2% and 15.4% to 2.2%, respectively. The offset distribution turned out to be random in the 3D coordinate. This study provided the quantitative data that support the large individual field dose difference mainly stems from possible geometric errors (e.g., random setup errors) under the influence of steep dose gradients of IMRT field.

• 한국콘텐츠학회논문지
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• 제14권1호
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• pp.356-363
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• 2014

소아 CT 촬영시 피폭선량을 저감시킬 수 있는 조건을 찾기 위하여 pediatric phantom을 이용하여 소아 방사선량을 비교 분석하였다. 관전류변동제어(tube current modulation:TCM) 방식과 low dose CT protocol(LDCTP)에 따라 소아 검사를 시행하였으며, 검사는 brain, chest, abdomen-pelvis 부위를 전산화 단층촬영 장치를 이용한 3개의 검사 프로토콜을 사용하였다. 거의 모든 MDCT 장치는 volume CT dose index(CTDIvol), dose length product(DLP)와 유효선량 평가 결과를 기록, 보관하고 있으며, 이러한 정보들은 환자들의 방사선 노출 및 위험도를 평가하는 데 필수적이다. 방사선 노출 위험도를 감소시키기 위해서 적정화 및 정당화 원칙을 반드시 준수해야 한다. 관전압(kV)에 따른 TCM 방식을 사용하였을 경우 kV가 낮아질수록 유효선량이 낮아지는 경향을 나타내었으며, low dose CT protocol을 사용한 경우가 유효선량이 상대적으로 더 적은 것을 알 수 있었다. 또한 평균 유효선량은 brain, chest, abdomen-pelvis CT의 결과가 독일의 reference dose 보다 각각 47%, 13.8%, 25.7%로 더 낮게 나타났고. 영국의 reference dose와 비교해도 55.7%, 10.2%, 43.6%에 불과했다. 결론적으로 선량 감소를 위해 주의할 것은 body-weight based tube current adaption을 포함한 TCM, 그리고 LDCTP 등 모든 선량 감소 방안을 이용하여야 한다.

• 대한의생명과학회지
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• 제12권3호
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• pp.289-301
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• 2006

Cardiopulmonary bypass (CPB) for cardiac surgery triggers the production and release of numerous chemotactic substances and cytokines, ensuing systemic inflammatory response that leads to postoperative major organ dysfunction. Traditionally, corticosteroids (steroid) have been administered to patients undergoing cardiac surgery to ward off these detrimental physiologic alterations. However, the majority of the studies have been performed on adult patients with high-dose steroid. We carried out a randomized, prospective, double-blind study to compare the efficacy of low-dose steroid with that of high-dose steroid and to determine the adequate dose of pretreated-steroid for prophylactic effects in pediatric cardiac surgery. Thirty pediatric patients scheduled for elective cardiac surgery were randomly assigned to two groups; fifteen patients received low-dose methylprednisolone (10mg/kg intravenously, n=15, low-dose group) and the others received high-dose methylprednisolone (30mg/kg intravenously, n=15, high-dose group) 1 hour prior to CPB. Arterial blood samples were taken before CPB (Pre-CPB), 10 minutes after start of CPB (CPB-10), and immediately after CPB-end (CPB-OFF) for measuring total leukocyte counts (T-WBC) and diff-counts, platelet counts, interleukin-6 (IL-6), myeloperoxidase (MPO), total antioxidant (TAO), neuron-specific enolase (NSE), troponin I (TNI), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, and blood urea nitrogen (BUN) levels. Other parameters such as volumes of urine output, pulmonary index $(PI,\;PaO_2/FiO_2)$, mechanical ventilating period, intensive care unit (ICU)-staying period, postoperative complications (fever, wound problem), postoperative 24 hrs and total volumes in blood loss, and hospitalized days were also assessed. All parameters were compared between two groups. There were no significant differences in T-WBC counts, monocyte fraction, platelet counts, TA levels, NSE levels, creatinine levels, BUN levels, the volumes of total urine output, PI, the incidences of fever and wound problem, postoperative 24hrs- and total-blood loss volumes and ICU-staying period between two groups (P>0.05). At CPB-OFF, neutrophil fraction, MPO level, TNI level, and AST level were higher in the high-dose group than in the low-dose group (P<0.05). IL-6 level at CPB-10 was higher in the high dose-group than in the low-dose group (P<0.05). Furthermore, mechanical ventilating periods and hospitalized days of the high-dose group were significantly longer than those of low-dose group (P<0.05). The high-dose group had significantly low lymphocyte fi-action at CPB-OFF compared with the low-dose group (P<0.001). These findings suggest that pretreatment of high-dose steroid is not superior to that of low-dose steroid regrading its potential benefits in pediatric cardiac surgery. Therefore, the conventional strategy of steroid treatment, high-dose pretreatment, should be modified in the cardiac surgery with CPB. However, further studies must be performed on the larger number of patients in as much as small number of patients in this study.

• 방사선산업학회지
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• 제11권3호
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• pp.131-137
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• 2017

To compare the radiation dose and image noise of low dose computed tomography (CT) and high resolution CT using the fixed tube current technique and automatic tube current modulation (CARE Dose 4D). Chest CT and human anthropomorphic phantom were used the RPL (radiophotoluminescence) dosimeters. For image evaluation, standard deviation of mean CT attenuation coefficient and CT attenuation coefficient was measured using ROI analysis function. The effective dose was calculated using CTDIvol and DLP. CARE Dose 4D was reduced by 74.7% and HRCT by 64.4% compared to the fixed tube current technique in low dose CT of chest phantom. In CTDIvol and DLP, the dose of CARE Dose 4D was reduced by fixed tube current technique. For effective dose, CARE Dose 4D was reduced by 47% and HRCT by 46.9% compared to the fixed tube current method, and the dose of CARE Dose 4D was significantly different (p<.05). Noise in the image was higher than that in the fixed tube current technique. Noise difference in the image of CARE Dose 4D in low dose CT was significant (p<.05). The low radiation dose and the noise difference of the CARE Dose 4D were compared with the fixed tube current technique in low dose CT and HRCT using chest phantom. The radiation doses using CARE Dose 4D were in accordance with the national and international dose standards. CARE Dose 4D should be applied to low dose CT and HRCT for clinical examination.

• 한국방사선학회논문지
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• 제16권1호
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• pp.45-51
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• 2022

본 연구는 Chest CT에서 Care Dose 4D+Care kV System을 사용하여 촬영할 때와 CARE DOSE 4D 기능만을 사용했을 때, 그리고 Care Dose 4D와 관전압을 각각 80 kVp, 100 kVp, 120 kVp, 140 kVp로 변화를 주고 검사했을 때의 DLP값과 팬텀의 입사표면선량, 화질을 비교하여 최소의 선량으로 가장 최상의 화질을 유지할 수 있는 방법을 찾아보고자 하였다. DLP값은 Chest Care Dose 4D + Care kV semi 100으로 촬영하였을 때 6.727%, Chest Care Dose 4D + Care kV 로 촬영하였을 때 6.481% 감소하는 것으로 나타났다. Chest Non을 기준으로 입사표면선량에서 Chest Care Dose 4D + Care kV semi 100으로 검사하였을 때 16.519%, Chest Care Dose 4D + Care kV 로 검사하였을 때 15.705% 감소하는 것으로 나타났다. 영상의 화질에 대한 비교에서 Chest Non과 비교해서 Care Dose 4D + Care kV를 포함한 모든 촬영조건에서 SNR값과 CNR값을 비교한 결과 P>0.05로 유의한 차이가 없는 것으로 나타났다. Chest CT에서 Chest Care Dose 4D + Care kV를 사용해서 촬영한 결과 수동으로 kV와 mAS를 조정해서 얻은 최상의 조건의 결과 값과 비슷하게 피폭선량이 감소한 것으로 나타났으며, 영상의 SNR과 CNR에서도 유의한 차이가 없는 것으로 나타났다. Chest Care Dose 4D + Care kV 기능을 사용한다면 영상의 화질을 유지하면서 환자피폭을 줄일 수 있는 좋은 방법이라 생각된다.

• Nuclear Engineering and Technology
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• 제52권5호
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• pp.956-963
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• 2020

Dose optimization for Radioactive Occupational Personal (ROP) is an important subject in nuclear and radiation safety field. The geometric environment of a nuclear facility is complex and the work area is radioactive, so traditional navigation model and radioactive data field cannot form an effective environment model for dose assessment and dose optimization. The environment model directly affects dose assessment and indirectly affects dose optimization, this is an urgent problem needed to be solved. Therefore, this paper focuses on an environment model used for Dose Assessment and Dose Optimization (DA&DO). We designed a multi-layer radiation field coupling modeling method, and then explored the influence of the environment model to DA&DO by virtual simulation. Then, a simulation test is done, the multi-layer radiation field coupling model for nuclear facilities is demonstrated to be effective for dose assessment and dose optimization through the experiments and analysis.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.958-967
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• 2023

This work studies the defect features in a dilute FeMnNi alloy by an Object Kinetic Monte Carlo (OKMC) model based on the "grey-alloy" method. The dose rate effect is studied at 573 K in a wide range of dose rates from 10^-8 to 10^-4 displacement per atom (dpa)/s and demonstrates that the density of defect clusters rises while the average size of defect clusters decreases with increasing dose rate. However, the dose-rate effect decreases with increasing irradiation dose. The model considered two realistic mechanisms for producing <100>-type self-interstitial atom (SIA) loops and gave reasonable production ratios compared with experimental results. Our simulation shows that the proportion of <100>-type SIA loops could change obviously with the dose rate, influencing hardening prediction for various dose rates irradiation. We also investigated ways to compensate for the dose rate effect. The simulation results verified that about a 100 K temperature shift at a high dose rate of 1×10^-4 dpa/s could produce similar irradiation microstructures to a lower dose rate of 1×10^-7 dpa/s irradiation, including matrix defects and deduced solute migration events. The work brings new insight into the OKMC modeling and the dose rate effect of the Fe-based alloys.