• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.274-281
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• 2016

Background: Whole-body counters are widely used to evaluate internal contamination of the internal presence of gamma-emitting radionuclides. In internal dosimetry, it is a basic requirement that quality control procedures be applied to verify the reliability of the measured results. The implementation of intercomparison programs plays an important role in quality control, and the accuracy of the calibration and the reliability of the results should be verified through intercomparison. In this study, we evaluated the reliability of 2 whole-body counting systems using 2 calibration methods. Materials and Methods: In this study, 2 whole-body counters were calibrated using a reference male bottle manikin absorption (BOMAB) phantom and a Radiation Management Corporation (RMC-II) phantom. The reliability of the whole-body counting systems was evaluated by performing an intercomparison with International Atomic Energy Agencyto assess counting efficiency according to the type of the phantom. Results and Discussion: In the analysis of counting efficiency using the BOMAB phantom, the performance criteria of the counters were satisfied. The relative bias of activity for all radionuclides was -0.16 to 0.01 in the Fastscan and -0.01 to 0.03 in the Accuscan. However, when counting efficiency was analyzed using the RMC- II phantom, the relative bias of $^{241}Am$ activity was -0.49 in the Fastscan and 0.55 in the Accuscan, indicating that its performance criteria was not satisfactory. Conclusion: The intercomparison process demonstrated the reliability of whole-body counting systems calibrated with a BOMAB phantom. However, when the RMC-II phantom was used, the accuracy of measurements decreased for low-energy nuclides. Therefore, it appears that the RMC-II phantom should only be used for efficiency calibration for high-energy nuclides. Moreover, a novel phantom capable of matching the efficiency of the BOMAB phantom in low-energy nuclides should be developed.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4167-4172
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• 2023

Miniaturized tissue equivalent proportional counters (mini-TEPCs) are proper for radiation dosimetry in medical application because the small size of the dosimeter could prevent pile-up effect under the high intensity of therapeutic beam. However, traditional methods of calibrating mini-TEPCs using internal alpha sources are not feasible due to their small size. In this study, we investigated the use of electron and proton edges on Monte Carlo-generated lineal energy spectra as markers for calibrating a 0.9 mm diameter and length mini-TEPC. Three possible markers for each spectrum were calculated and compared using different simulation tools. Our simulations showed that the electron edge markers were more consistent across different simulation tools than the proton edge markers, which showed greater variation due to differences in the microdosimetric spectra. In most cases, the second marker, y_δδ, had the smallest uncertainty. Our findings suggest that the lineal energy spectra from mini-TEPCs can be calibrated using Monte Carlo simulations that closely resemble real-world detector and source geometries.

• Journal of Radiation Protection and Research
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• 제47권3호
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• pp.111-133
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• 2022

The exciting advancement related to the "modeling of digital human" in terms of a computational phantom for radiation dose calculations has to do with the latest hype related to deep learning. The advent of deep learning or artificial intelligence (AI) technology involving convolutional neural networks has brought an unprecedented level of innovation to the field of organ segmentation. In addition, graphics processing units (GPUs) are utilized as boosters for both real-time Monte Carlo simulations and AI-based image segmentation applications. These advancements provide the feasibility of creating three-dimensional (3D) geometric details of the human anatomy from tomographic imaging and performing Monte Carlo radiation transport simulations using increasingly fast and inexpensive computers. This review first introduces the history of three types of computational human phantoms: stylized medical internal radiation dosimetry (MIRD) phantoms, voxelized tomographic phantoms, and boundary representation (BREP) deformable phantoms. Then, the development of a person-specific phantom is demonstrated by introducing AI-based organ autosegmentation technology. Next, a new development in GPU-based Monte Carlo radiation dose calculations is introduced. Examples of applying computational phantoms and a new Monte Carlo code named ARCHER (Accelerated Radiation-transport Computations in Heterogeneous EnviRonments) to problems in radiation protection, imaging, and radiotherapy are presented from research projects performed by students at the Rensselaer Polytechnic Institute (RPI) and University of Science and Technology of China (USTC). Finally, this review discusses challenges and future research opportunities. We found that, owing to the latest computer hardware and AI technology, computational human body models are moving closer to real human anatomy structures for accurate radiation dose calculations.

• 대한핵의학회지
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• 제29권3호
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• pp.343-349
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• 1995

배경 : 방사선 외부 피폭에 대한 생물학적 선량측정방법에는 혈액학적 지표인 림프구 변화와 세포유전학적 지표인 염색체 분석을 통한 Ydr값이 가장 많이 사용되고 있다. 방사성 옥소 투여시와 같은 방사선 내부 피폭에 대해서는 생물학적 선량측정 방법에 대한 연구가 미흡하여 피폭정도는 물론 방사성 옥소 투여용량을 반영할 수 있는지의 여부도 알려져 있지 못하다. 목적 : 갑상선 질환자에게 방사성 옥소 투여후 림프구 변화와 Ydr값을 추적관찰하여 이들을 방사선 내부 피폭에 대한 지표로 이용할 수 있는지 알아보고자 하였다. 방법 : 갑상선 기능항진증 5명과 갑상선암 수술을 받은 35명의 환자를 대상으로 방사성 옥소 투여후 말초혈액 림프구 수를 2개원이상 추적검사 하였고, 림프구의 염색체 분석을 통해 Ydr값을 구했다. 결과: 1) 림프구 수는 방사성 옥소 투여 2주후 부터 감소되기 시작하여 6주와 8주후에 최대로 감소된후 점차 회복되었다. 2) 방사성 옥소량이 증가할 수록 림프구 수는 감소했다 (P<0.01) 3) Ydr값은 2주-8주 사이에는 대체로 일정하였다. 4) 방사성옥소 투여량에 따른 최대 Ydr값의 변화는 유의한 상관관계를 보였다 (p<0.00) 5) 2주째 Ydr값은 방사성옥소 투여량이 증가할 수록 증가하였다 (p<0.00) 6) 2주째 Ydr값은 2주째 림프구 수의 감소정도와 비례관계를 보였다 (p<0.00) 결론: 1) 방사성 옥소의 통상적 치료용량은 일시적 골수부전과 경도의 염색체이상을 초래하므로 8주 이상의 면밀한 추적관찰이 요구된다. 2) 생물학적 선량측정 방법으로서의 최대 림프구 감소치와 2주째 Ydr값과 최대 Ydr값은 방사성옥소 투여용량을 반영하는 지표로 사용할 수 있다.

• Journal of Radiation Protection and Research
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• 제34권3호
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• pp.129-136
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• 2009

국내 원전의 계획예방정비기간 중에 원자로계통의 개방과정에서 원자로건물내 공기 중으로 누설된 $^{131}I$의 체내 흡입으로 원전종사자의 내부피폭이 발생하였다. 이에 따라 원전에서 보유하고 있는 전신계측기(Whole body counter)를 이용하여 내부방사능을 측정하였다. 이들 측정값을 근거로 국제방사선방호위원회(ICRP)의 내부피폭 선량평가 지침을 적용하여 섭취량을 산정하고, 내부 피폭 방사선량을 평가하였다. $^{131}I$은 체내에서 섭취와 배설이 빠르고 갑상선으로 재축적이 일어나기 때문에 섭취 후 측정시점에 따라 섭취량이 차이를 보였다. 또한 ICRP 간행물에서 $^{131}I$의 전선에 대한 섭취잔류분율 자료를 제공하고 있지 않아 갑상선 섭취잔류분율 자료를 이용함으로써 섭취량 평가에서 오차를 나타내었다. 이에 따라 수계산과정으로 섭취량을 산정하고 예탁유효선량을 평가하였다. 한편 전선에 대한 섭취잔류분율을 새로 계산하였으며, 이 결과를 검증하였다. 또한 국제적으로 이용되고 있는 내부 피폭 선량평가 전신코드들 이용하여 섭취량 산정과 내부피폭 선량평가 평가결과에 대한 비교 계산이 병행하여 이루어졌다.

• Journal of Radiation Protection and Research
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• 제49권1호
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• pp.50-64
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• 2024

Background: The reference dose coefficients (DCs) of the International Commission on Radiological Protection (ICRP) have been widely used to estimate organ doses of individuals for risk assessments. This approach has been well accepted because individual anatomy data are usually unavailable, although dosimetric uncertainty exists due to the anatomical difference between the reference phantoms and the individuals. We attempted to quantify the individual variation of organ doses for photon external exposures by calculating and comparing organ DCs for 30 individuals against the ICRP reference DCs. Materials and Methods: We acquired computed tomography images from 30 patients in which eight organs (brain, breasts, liver, lungs, skeleton, skin, stomach, and urinary bladder) were segmented using the ImageJ software to create voxel phantoms. The phantoms were implemented into the Monte Carlo N-Particle 6 (MCNP6) code and then irradiated by broad parallel photon beams (10 keV to 10 MeV) at four directions (antero-posterior, postero-anterior, left-lateral, right-lateral) to calculate organ DCs. Results and Discussion: There was significant variation in organ doses due to the difference in anatomy among the individuals, especially in the kilovoltage region (e.g., <100 keV). For example, the red bone marrow doses at 0.01 MeV varied from 3 to 7 orders of the magnitude depending on the irradiation geometry. In contrast, in the megavoltage region (1-10 MeV), the individual variation of the organ doses was found to be negligibly small (differences <10%). It was also interesting to observe that the organ doses of the ICRP reference phantoms showed good agreement with the mean values of the organ doses among the patients in many cases. Conclusion: The results of this study would be informative to improve insights in individual-specific dosimetry. It should be extended to further studies in terms of many different aspects (e.g., other particles such as neutrons, other exposures such as internal exposures, and a larger number of individuals/patients) in the future.

• 한국의학물리학회지:의학물리
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• 제31권3호
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• pp.81-98
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• 2020

This review aims to provide a brief, comprehensive overview of advanced technologies of nuclear medicine physics, with a focus on recent developments from both hardware and software perspectives. Developments in image acquisition/reconstruction, especially the time-of-flight and point spread function, have potential advantages in the image signal-to-noise ratio and spatial resolution. Modern detector materials and devices (including lutetium oxyorthosilicate, cadmium zinc tellurium, and silicon photomultiplier) as well as modern nuclear medicine imaging systems (including positron emission tomography [PET]/computerized tomography [CT], whole-body PET, PET/magnetic resonance [MR], and digital PET) enable not only high-quality digital image acquisition, but also subsequent image processing, including image reconstruction and post-reconstruction methods. Moreover, theranostics in nuclear medicine extend the usefulness of nuclear medicine physics far more than quantitative image-based diagnosis, playing a key role in personalized/precision medicine by raising the importance of internal radiation dosimetry in nuclear medicine. Now that deep-learning-based image processing can be incorporated in nuclear medicine image acquisition/processing, the aforementioned fields of nuclear medicine physics face the new era of Industry 4.0. Ongoing technological developments in nuclear medicine physics are leading to enhanced image quality and decreased radiation exposure as well as quantitative and personalized healthcare.

• 한국의학물리학회지:의학물리
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• 제16권2호
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• pp.89-96
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• 2005

본 연구는 호흡에 따라 내부 장기가 움직일 때, 내부 장기가 가장 안정적인 구간의 문턱 값(threshold)을 시간으로 설정한 후 선량분포에 대한 연구를 수행하였다. 일반적으로 정상적인 호흡주기 중에서 시간대비 내부 장기 움직임이 호기 상태에서 적게 나타난다. 그러므로 시간동기 문턱 값(time gating threshold, TGT)은 내부 장기 움직임이 가장 적은 호기 시 1 초 동안 움직일 때의 선량분포를 평가하였다. TGT를 설정했을 때 선량분포를 비교하기 위해 다음 조건으로 방사선을 조사하였다. 내부 장기가 1) 고정된 상태, 2) 문책 값 범위 내에서 움직일 때, 3) 문턱 값 범위 밖에서 움직일 때, 각각의 내부 장기 움직임 조건을 구동팬톰시스템으로 모사하였다. 그리고 필름 선량 측정법(film dosimetry)을 이용하여 비교 평가하였다. TGT를 1초로 설정하고 내부적 움직임을 고려하여 선량분포를 획득했을 때 치료시간은 증가하였다. 그러나 TGT를 1초로 설정한 것은 내부적 움직임을 고려하지 않은 선량분포 즉, 치료 조사면 내에 장기의 움직임이 없을 때와 비슷한 선량분포를 얻을 수 있었다. 그리고 문턱 詰없이 내부 장기가 움직일 때와 비교해서 반음영 영역에 불필요한 선량을 줄일 수 있었다. 또한 치료시간을 줄이기 위해서 문턱 값을 1.4초로 설정했을 때가 1초로 설정했을 때보다 시간 비에 따른 선량분포에 대해 효과적인 결과를 얻지 못했다. 즉, 시간은 줄었지만 치료영역 밖에 많은 선량이 분포하였다. 임상적으로 TGT를 설정해서 방사선 치료를 하기 위해서는 수학적인 계산 방법에 의한 내부 장기의 움직임을 표현하는 것이 아니라 실측에 의해서 모든 환자의 외부 움직임과 내부 움직임을 측정해야 한다. 또한 내부와 외부 움직임의 상관관계를 분석해서 환자의 호흡주기에 따른 내부 장기의 움직임 중에 이상적인 위치에서 문책 값을 설정 후 방사선치료를 시행하면 정상조직은 낮은 선량이 분포하면서 치료성적이 향상될 것이라 예상된다.

• 대한방사선기술학회지:방사선기술과학
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• 제28권2호
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• pp.117-122
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• 2005

1999년 개정된 국내 원자력법 시행령 제2조 5항에 의하면 2003년부터 원전 작업종사자들에 대해 외부 피폭 선량뿐만 아니라 내부피폭 선량도 합산하여 평가하도록 하였으며 또한 각 선량평가에 대한 오차도 50% 이내로 유지되어야 한다고 규정한 바 있어 전신이나 갑상선 계측기와 같은 내부피폭선량 측정 장비의 정밀한 계측이 요구되고 있다. 이러한 국내 원자력법의 개정에 부합하여 본 연구에서는 내부피폭 선량측정 결과치의 정확도를 향상시키기 위해서 현재 개발 중인 갑상선 내부피폭선량 측정 시스템의 검출효율을 계산하기 위한 몬테카를로 모의실험 코드(CALEFF)를 개발하였으며, 이 코드를 사용하여 다양한 실험조건에서 검출효율을 계산하였다. 향후 갑상선 내부피폭선량 측정 시스템의 보정인자로 사용하고자 한다.

• Asian Pacific Journal of Cancer Prevention
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• 제16권8호
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• pp.3257-3265
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• 2015

Background: Radiotherapy is an important treatment of choice for breast cancer patients after breast-conserving surgery, and we compare the feasibility of using dual arc volumetric modulated arc therapy (VMAT2), single arc volumetric modulated arc therapy (VMAT1) and Multi-beam Intensity Modulated Radiotherapy (M-IMRT) on patients after breast-conserving surgery. Materials and Methods: Thirty patients with breast cancer (half right-sided and half left-sided) treated by conservative lumpectomy and requiring whole breast radiotherapy with tumor bed boost were planned with three different radiotherapy techniques: 1) VMAT1; 2) VMAT2; 3) M-IMRT. The distributions for the planning target volume (PTV) and organs at risk (OARs) were compared. Dosimetries for all the techniques were compared. Results: All three techniques satisfied the dose constraint well. VMAT2 showed no obvious difference in the homogeneity index (HI) and conformity index (CI) of the PTV with respect to M-IMRT and VMAT1. VMAT2 clearly improved the treatment efficiency and can also decrease the mean dose and V5Gy of the contralateral lung. The mean dose and maximum dose of the spinal cord and contralateral breast were lower for VMAT2 than the other two techniques. The very low dose distribution (V1Gy) of the contralateral breast also showed great reduction in VMAT2 compared with the other two techniques. For the ipsilateral lung of right-sided breast cancer, the mean dose was decreased significantly in VMAT2 compared with VMAT1 and M-IMRT. The V20Gy and V30Gy of the ipsilateral lung of the left-sided breast cancer for VMAT2 showed obvious reduction compared with the other two techniques. The heart statistics of VMAT2 also decreased considerably compared to VMAT1 and M-IMRT. Conclusions: Compared to the other two techniques, the dual arc volumetric modulated arc therapy technique reduced radiation dose exposure to the organs at risk and maintained a reasonable target dose distribution.