• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1814-1820
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• 2018

With the publication of TRS-483 in late 2017 the IAEA has established an international code of practice for reference dosimetry in small and non-standard fields based on a formalism first suggested by Alfonso et al. in 2008. However, data on beam quality correction factors ($k^{f_{msr},f_{ref}}_{Q_{msr},Q_0}$) for the Leksell Gamma $Knife^{(R)}$ $Perfexion^{TM}$ is scarce and what little data is available was obtained under conditions not necessarily in accordance with the IAEA's recommendations. This study constitutes the first systematic attempt to calculate those correction factors by applying the new code of practice to Monte Carlo simulation using the GEANT4 toolkit. $k^{f_{msr},f_{ref}}_{Q_{msr},Q_0}$ values were determined for three common ionization chamber detectors and five different phantom materials, with results indicating that in most phantom materials, all chambers were well suited for reference dosimetry with the Gamma $Knife^{(R)}$. Similarities and differences between the results of this study and previous ones were also analyzed and it was found that the results obtained herein were generally in good agreement with earlier PENELOPE and EGSnrc studies.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.255-259
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• 2002

To reduce the uncertainty in the calibration of radiation beams, absorbed dose to water for high energy electrons is recommended as the standards and reference absorbed dose by AAPM Report no.51 and IAEA Technical Reports no.398. In these recommendations, water is, defined as the reference medium, however, the water substitute solid phantoms are discouraged. Nevertheless, when accurate chamber positioning in water is not possible, or when no waterproof chamber is available, their use is permitted at beam qualities R$\_$50/ < 4 g/cm$^2$ (E$\_$0/ < 10 MeV). For the electron dosimetry using solid phantom, a depth-scaling factor is used for the conversion of depth in solid phantoms to depth in water, and a fluence-scaling factor is used for the conversion of ionization chamber reading in plastic phantom to reading in water. In this work, the properties, especially depth-scaling factors c$\_$p1/ and fluence-scaling factors h$\_$pl/ of several commercially available water substitute solid phantoms were determined, and the electron dosimetry using these scaling method was evaluated. As a result, it is obviously that dose-distribution in solid phantom can be converted to appropriate dose-distribution in water by means of IAEA depth-scaling.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2599-2605
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• 2022

The Korea Retrospective Dosimetry network (KREDOS) performed an inter-laboratory comparison to confirm the harmonization and reliability of the results of retrospective dosimetry using mobile phone. The mobile phones were exposed to ¹⁹²Ir while attached to the human phantoms in the field experiment, and the exposure doses read by each laboratory were compared. This paper describes the reference dosimetry performed to present the reference values for inter-comparison and to obtain additional information about the dose distribution. Reference dosimetry included both measurement using LiF:Mg,Cu,Si and calculation via MCNP simulation to allow a comparison of doses obtained with the two different methodologies. When irradiating the phones, LiF elements were attached to the phones and phantoms and irradiated at the same time. The comparison results for the front of the phantoms were in good agreement, with an average relative difference of about 10%, while an average of about 16% relative difference occurred for the back and side of the phantom. The differences were attributed to the different characteristics of the physical and simulated phantoms, such as anatomical structure and constituent materials. Nevertheless, there was about 4% of under-estimation compared to measurements in the overall linear fitting, indicating the calculations were well matched to the measurements.

• 대한방사선기술학회지:방사선기술과학
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• 제46권3호
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• pp.239-246
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• 2023

In this study, we assessed the effect of reduction of tumor volume in the head and neck cancer by using RANDO phantom in Static Intensity-Modulated Radiation Therapy (S-IMRT) and Volumetric-Modulated Arc Therapy (VMAT) planning. RANDO phantom's body and protruding volumes were delineated by using Contour menu of Eclipse™ (Varian Medical System, Inc., Version 15.6, USA) treatment planning system. Inner margins of 2 mm to 10 mm from protruding volumes of the reference were applied to generate the parameters of reduced volume. In addition, target volume and Organ at Risk (OAR) volumes were delineated. S-IMRT plan and VMAT plan were designed in reference. These plans were assigned in the reduced volumes and dose was calculated in reduced volumes using preset Monitor unit (MU). Dose Volume Histogram (DVH) was generated to evaluate treatment planning. Conformity Index (CI) and R² in reference S-IMRT were 0.983 and 0.015, respectively. There was no significant relationship between CI and the reduced volume. Homogeneity Index (HI) and R² were 0.092 and 0.960, respectively. The HI increased when volume reduced. In reference VMAT, CI and R² were 0.992 and 0.259, respectively. There was no relationship between the volume reduction and CI. On the other hand, HI and R² were 0.078 and 0.895, respectively. The value of HI increased when the volume reduced. There was significant difference (p<0.05) between parameters (D_mean and D_max) of normal organs of S-IMRT and VMAT except brain stem. Volume reduction affected the CI, HI and OAR dose. In the future, additional studies are necessary to incorporate the reduction of the volume in the clinical setting.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4698-4707
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• 2022

As part of the ICRP Task Group 103 project, we developed ten thyroid models for the pediatric mesh-type reference computational phantoms (MRCPs). The thyroid is not only a radiosensitive target organ needed for effective dose calculation but an important source region particularly for radioactive iodines. The thyroid models for the pediatric MRCPs were constructed by converting those of the pediatric voxel-type reference computational phantoms (VRCPs) in ICRP Publication 143 to a high-quality mesh format, faithfully maintaining their original topology. At the same time, we improved several anatomical parameters of the thyroid models for the pediatric MRCPs, including the mass, overlying tissue thickness, location, and isthmus dimensions. Absorbed doses to the thyroid for the pediatric MRCPs for photon external exposures were calculated and compared with those of the pediatric VRCPs, finding that the differences between the MRCPs and VRCPs were not significant except for very low energies (<0.03 MeV). Specific absorbed fractions (target ⟵ thyroid) for photon internal exposures were also compared, where significant differences were frequently observed especially for the target organs/tissues close to the thyroid (e.g., a factor of ~1.2-~327 for the thymus as a target) due mainly to anatomical improvement of the MRCP thyroid models.

• 한국의학물리학회지:의학물리
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• 제28권4호
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• pp.190-196
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• 2017

For the $ViewRay^{(R)}$ system (ViewRay Inc., Cleveland, OH, USA) which is representative of magnetic resonance (MR) guided radiotherapy machine, it is important to evaluate effectiveness of AAPM's TG-51 protocol and the effect of the magnetic field on absolute dosimetry. In order to measure the absolute dose, MR-compatible chamber and water phantom system manufactured in this study were used. The materials of the water phantom system were plastic of polymethyl methacrylate (PMMA) and non-ferrous materials. Due to the inherent feature of the $ViewRay^{(R)}$, all Co-60 sources are not located at gantry angle of $0^{\circ}$ while being located at gantry angle of $90^{\circ}$. For this reason, absolute dosimetry was performed based on the measurements in solid water phantom (SWP) and water which determine the SWP to water correction factor. For evaluation of output constancy with gantry angle, measurements were made with ionization chamber inserted in cylindrical water-equivalent phantom. For measured doses in water, the values of dose deviation according to a reference dose of 200 cGy for Head 1, Head 2 and Head 3 were -0.27%, -0.45% and -0.22%, respectively. For measured doses in SWP, the values of dose deviation according to a reference dose of 200 cGy for Head 1, Head 2 and Head 3 were -1.91%, -2.07% and -1.84%, respectively. All values of dose measured in SWP tended to be less than those measured in water by -1.63%. With the reference gantry angles of $0^{\circ}$ and $90^{\circ}$, the maximum values of deviation for Head 1, Head 2 and Head 3 were 0.48%, 1.06% and 0.40%, respectively. The measurement agreement is within the range of results obtainable for conventional treatment machines. The low strength of the magnetic field does not affect dose measurements. Using the SWP to water correction factor, absolute doses for $ViewRay^{(R)}$ system can be measured.

• 대한방사선기술학회지:방사선기술과학
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• 제40권4호
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• pp.595-603
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• 2017

본 연구는 파킨슨질환의 진행 정도를 평가할 수 있는 선조체를 모사한 brain 팬텀을 직접 제작하여, PET-CT검사 시 최적의 영상의 질을 유지하면서 CT 스캔에 의한 brain 선량 저감을 위한 가능성을 평가하였다. 팬텀의 hot sphere와 background (radi oacti vi ty rati o 3:1)에 $^{18}F$ FP-CIT를 주입하고, 관전압(100, 120 kVp)과 관전류(80, 140, 200 mAs)의 조건을 변화시키며 CT 스캔을 실험하였다(기준조건; 120 kVp, 140 mAs). 각 조건에 따라 예상유효선량을 conversion factor를 적용해 계산하였고, SNR과 CRChot의 영상평가 인자를 설정하여 영상의 질을 평가하였다. 실험결과 CT 촬영 기준조건 이하에서의 예상유효선량은 최소 10%에서 최고 60% 정도 감소하였고, 기준조건 이상에서의 예상유효선량은 40% 증가하였다. 또한 PET 영상의 SNR과 CRChot의 유의한 차이는 없었으므로, 관전압과 관전류의 감소에 따라 brain 선량이 감소함을 확인하였다. 이와 동시에 스캔 조건의 변화에도 불구하고 SNR과 CRChot 측면에서의 영상의 질에는 유의한 변화가 없었다. 이러한 사실은 낮은 선량 조건으로도 기존의 선량 조건으로 획득한 영상의 질 수준을 얻을 수 있었으므로, 추후 brain PET-CT 스캔의 선량감소와 동시에 영상의 질 향상에 관한 연구의 기초자료로 활용이 가능할 것으로 사료된다.

• Imaging Science in Dentistry
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• 제32권3호
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• pp.135-139
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• 2002

Purpose: To determine the proper reference step wedge for digital Cu-Equivalent Image analyzing systems for measurement of bone density. Meterials and Methods : Radiograms of lumbar vertebrae phantom (1g/㎠) with 3 test copper step wedges of 0.03, 0.05 and, 0.1 mm thickness unit were taken and analyzed using NIH image software on a Macintosh personal computer. Measured densities of the lumbar areas in the Cu-Equivalent images made by utilizing 3 different copper stepwedges were compared with a known bone density. Results: The values of r2 for all copper equivalent images were over 0.99. The mean Cu-Eq value of lumbar in copper equivalent image made by a 0.1 mm copper stepwedge was 0.22 ± 0.06 mm and converted to hydroxyapatite density of 1.03 g/㎠. The stepwedges of 0.03 and 0.05 mm produced results having higher values than the actual known bone density. They did not show the blue and green color level that appeared in lumbar on color enhanced image. Conclusion : A copper stepwedge of adequate thickness and range of steps which can express the range of density of bone being measured should be used.

• 한국의학물리학회지:의학물리
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• 제23권3호
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• pp.199-208
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• 2012

전신에 대해 방사선에 민감한 주요장기가 미리 정의된 인체 전산팬텀(compuational human phantom)은 의료분야에서 방사선 치료에 의한 이차암 위험도 평가 및 진단방사선에 의한 유효선량 평가 등에 유용하게 활용될 수 있다. 본 연구에서는 한국인 여성사체에 대한 고해상도 연속절단면 컬러해부영상을 이용하여 장기 및 조직을 전신에 걸쳐 약 2 mm 간격으로 정밀하게 분할하였고, 이를 이용하여 몬테칼로 전산모사에 사용될 수 있는 VHK-Woman 복셀팬텀을 개발하였다. VKH-Woman 복셀팬텀은 키 160 cm, 몸무게 52.72 kg으로 한국인 여성의 표준체형에 가까우며, 유효선량을 계산할 수 있도록 ICRP 103에 제시된 27개 장기 및 기타 관심장기 12개를 포함한다. VKH-Woman의 복셀 해상도는 $1.976{\times}1.976{\times}2.0619mm^3$이며 복셀행렬의 크기는 $261{\times}109{\times}825$이고, 몬테칼로 코드에 입력하여 사용될 수 있도록 이진파일과 ASCII 파일 형식으로 데이터화되었다.

• Journal of Radiation Protection and Research
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• 제41권2호
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• pp.101-104
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• 2016

Background: To protect the public from natural radioactive materials, the 'Act on safety control of radioactive rays around living environment" was established in Korea. There is an annual effective dose limit of 1 mSv for products, but the activity concentration limit for products is not established yet. Materials and Methods: To suggest the activity concentration limits for consumer goods containing NORM, in this research, we assumed the "small room model" surrounding the ICRP reference phantom to simulate the consumer goods in contact with the human bodies. Using the Monte Carlo code MCNPX, we evaluate the effective dose rate for the ICRP reference phantom in a small room with dimension of phantom size and derived the activity concentration limit for consumer goods. Results and Discussion: The consumer goods have about 1600, 1200 and $19000Bq{\cdot}kg^{-1}$ for $^{226}Ra$, $^{232}Th$ and $^{40}K$, and the activity concentration limits are about six times comparing with the values of building materials. We applied the index to real samples, though we did not consider radioactivity of $^{40}K$, indexes of the some samples are more than 6. However, this index concept using small room model is very conservative, for the consumer goods over than index 6, it is necessary to reevaluate the absorbed dose considering real usage scenario and material characteristics. Conclusion: In this research, we derived activity concentration limits for consumer goods in contact with bodies and the results can be used as preliminary screening tool for consumer goods as index concept.