• Progress in Medical Physics
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• v.16 no.2
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• pp.62-69
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• 2005

The purpose of this study has been performed to investigate the possibility of external audit program using thermoluminescence dosimetry for electron beam in korea. The TLD system consists of LiF powder, type TLD-700 read with a PCL 3 reader. In order to determine a calibration coefficient of the TLD system, the reference dosimeters are irradiated to 2 Gy in a $^{60}CO$ beam at the KFDA The irradiation is performed under reference conditions is water phantom using the IAEA standard holder for TLD of electron beam. The energy correction factor is determined for LiF powder irradiated of dose to water 2 Gy in electron beams of 6, 9, 12, 16 and 20 MeV (Varian CL 2100C). The dose is determined according to the IAEA TRS-398 and by measurement with a PTW Roos type plane-parallel chamber. The TLD for each electron energy are positioned in water at reference depth. In this study, to verify of the accuracy of dose determination by the TLD system are performed through a 'blind' TLD irradiation. The results of blind test are $2.98\%,\;3.39\%\;and\;0.01\%(1\sigma)$ at 9, 16, 20 MeV, respectively. The value generally agrees within the acceptance level of $5\%$ for electron beam. The results of this study prove the possibility of the TLD quality assurance program for electron beams. It has contributed to the improvement of clinical electron dosimetry in radiotherapy centers.

• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.16-27
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• 2015

The design challenges when attempting to obtain sufficient strength for a deepwater steel catenary riser (SCR) include high stress near the hang-off location, an elevated beam-column buckling load due to the effective compression in the touchdown zone (TDZ), and increased stress and low-cycle fatigue damage in the TDZ. Therefore, a systematic strength analysis is required for the proper design of an SCR. However, deepwater SCR analysis is a new research area. Thus, the objective of this study was to develop an overall analysis procedure for a deepwater SCR. The structural behavior of a deepwater SCR under various environmental loading conditions was investigated, and a sensitivity analysis was conducted with respect to various parameters such as the SCR weight, weight of the internal contents, hang-off angle (HOA), and vertical soil stiffness. Based on a deepwater SCR design example, it was found that the maximum stress of an SCR occurred at a hang-off location under parallel loading direction with respect to the riser plane, except for a wave dominant dynamic survival loading condition. Furthermore, the tensile stress governed the total stress of the SCRs, whereas the bending stress governed the total stress at the TDZ. The weight of the SCR and internal contents affected the maximum stress of the SCR more than the HOA and vertical soil stiffness, because the weight of the SCR, including the internal contents, was directly related to its tensile stress.

• Progress in Medical Physics
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• v.2 no.2
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• pp.155-160
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• 1991

We have studied the effective point of measurement for cylindrical ion chamber in water phantom for medical electron beams. Markus parallel plate chamber water phantom are used for the measurement of depth dose to determine the depth of the effective point of measurement for various energies(for electron 6MeV, 9MeV, 12MeV, 16MeV, and 20MeV; Co-60; for photon 6MV, 15MV). Cylindrical ion chambes(PTW233643 with r=2.75mm, PR-05P with r=2mm, and PM30 wiht r=15mm are used for the measurement of depth dose by same mtethod and the values of d$\_$50/ and R$\_$p/ obtained by three cylindrical chambers were compared with those of a flat chamber. From this we could evaluate the effective measuring points of cylindrical ion chamber. The effective point of measurement was estimated as 0.4～0.6r shifted toward surface from the center of the chamber for electron beam, 0.3～0.7r for $\^$60/Co X-ray.

• The Journal of Korean Society for Radiation Therapy
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• v.14 no.1
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• pp.59-64
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• 2002

Purpose : In radiotherapy, various materials are used to located in treatment field unintentionally. It increases the dose delivered to the skin by interactions of the X-ray within the materials and occurs unwanted skin reaction.(due to the dose build-up effect) This aim of the this study is to measure the increase in skin dose when 13 materials are located in treatment field. Methods : Photon beam measurements were made using an plane-parallel chamber (Markus, PTW-Freiburg) in a polystyrene phantom. skin dose were measured using various overlaying 13 materials. a fixed geometry of a $10{\times}10cm$ field, a SSD=100cm and photon energy 4MV on Varian CLINAC 600C accelerator were used for all measurements. Results : There is an increase in skin dose for all materials($16.4{\sim}160.1\%$). As a percentage of maximum dose, the lowest skin dose were measured for the underwear with silk($43.2\%$) and the highest were measured for the 100m1 fluid-bag($96.6\%$) Conclusion : There is a significant increase in skin dose with 13 materials in the treatment field. a significant increase in skin dose can occur which could produce unwanted skin reaction. considerations for placement of 13 materials to be outside the treatment field whenever possible should be used to keep skin dose to a minimum level.

• Journal of the Korean Wood Science and Technology
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• v.39 no.2
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• pp.132-139
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• 2011

This study examined the characteristics of radio-frequency/vacuum dried Korean red pine ($Pinus$ $densoflora$) heavy timbers with 250 ${\times}$ 250 mm (S), 300 ${\times}$ 300 mm (L) in cross section and 300 mm in diameter, and 3,600 mm in length, which were subjected to compressive loading after a kerf pretreatment. The following results were obtained : The drying time was short and the drying rate was high in spite of the large cross section of specimens. The moisture gradient inall specimens was gentle in both longitudinal and transverse directions owing to dielectric heating. The shrinkage of the width in the direction perpendicular to was 21 percent ~ 76 percent of that of the thickness of square timbers in the direction parallel to the mechanical pressure. The casehardening for all specimens was very slight because of significantly reduced ratio of the tangential to radial shrinkage of specimens and kerfing. The surface checks somewhat severely occurred although the occurrence extent of the surface checks on the kerfed specimens was slight compared withthat on the control specimen.

• Progress in Medical Physics
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• v.19 no.1
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• pp.21-34
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• 2008

The parallel Monte Carlo electron and photon transport (PMCEPT) code [Kum and Lee, J. Korean Phys. Soc. 47, 716 (2006)] for calculating electron and photon beam doses has been developed based on the three dimensional geometry defined by computed tomography (CT) images and implemented on the Beowulf PC cluster. Understanding the limitations of Monte Carlo codes is useful in order to avoid systematic errors in simulations and to suggest further improvement of the codes. We evaluated the PMCEPT code by comparing its normalized depth doses for electron and photon beams with those of MCNP5, EGS4, DPM, and GEANT4 codes, and with measurements. The PMCEPT results agreed well with others in homogeneous and heterogeneous media within an error of $1{\sim}3%$ of the dose maximum. The computing time benchmark has also been performed for two cases, showing that the PMCEPT code was approximately twenty times faster than the MCNP5 for 20-MeV electron beams irradiated on the water phantom. For the 18-MV photon beams irradiated on the water phantom, the PMCEPT was three times faster than the GEANT4. Thus, the results suggest that the PMCEPT code is indeed appropriate for both fast and accurate simulations.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.260-262
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• 2002

An accurate measurement of dose distribution is indispensable to perform radiation therapy planning. A measurement technique using a radiographic film, which is called a film dosimetry, is widely used because it is easy to obtain a dose distribution with a good special resolution. In this study, we tried to develop an analyzing system for the film dosimetry using usual office automation equipments such as a personal computer and an image scanner. A film was sandwiched between two solid water phantom blocks (30 ${\times}$ 30 ${\times}$ 15cm). The film was exposed with Cobalt-60 ${\gamma}$-ray whose beam axis was parallel to the film surface. The density distribution on the exposed film was stored in a personal computer through an image scanner (8bits) and the film density was shown as the digital value with NIH-image software. Isodose curves were obtained from the relationship between the digital value and the absorbed dose calculated from percentage depth dose and absorbed dose at the reference point. The isodose curves were also obtained using an Isodose plotter, for reference. The measurements were carried out for 31cGy (exposure time: 120seconds) and 80cGy (exposure time: 300seconds) at the reference point. While the isodose curves obtained with our system were drawn up to 60% dose range for the case of 80cGy, the isodose curves could be drawn up to 80% dose range for the case of 31cGy. Furthermore, the isodose curves almost agreed with that obtained with the isodose plotter in low dose range. However, further improvement of our system is necessary in high dose range.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.373-375
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• 2002

4D CT is a dynamic volume imaging system of moving organs with an image quality comparable to conventional CT, and is realized with continuous and high-speed cone-beam CT. In order to realize 4D CT, we have developed a novel 2D detector on the basis of the present CT technology, and mounted it on the gantry frame of the state-of-the-art CT-scanner. In the present report we describe the design of the first model of 4D CT-scanner as well as the early results of performance test. The x-ray detector for the 4D CT-scanner is a discrete pixel detector in which pixel data are measured by an independent detector element. The numbers of elements are 912 (channels) ${\times}$ 256 (segments) and the element size is approximately 1mm ${\times}$ 1mm. Data sampling rate is 900views(frames)/sec, and dynamic range of A/D converter is 16bits. The rotation speed of the gantry is l.0sec/rotation. Data transfer system between rotating and stationary parts in the gantry consists of laser diode and photodiode pairs, and achieves net transfer speed of 5Gbps. Volume data of 512${\times}$512${\times}$256 voxels are reconstructed with FDK algorithm by parallel use of 128 microprocessors. Normal volunteers and several phantoms were scanned with the scanner to demonstrate high image quality.

• Journal of radiological science and technology
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• v.17 no.1
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• pp.55-63
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• 1994

We have conducted on experiment with a purpose to evaluate the performance of grids being used at hospitals in Seoul and adjacent cities of Seoul. The results are as follows; Reality of the grids use 1. The focused grids were 105 and the parallel grids were 6 among 111 grids subject to experimenting. 2. The grid interspace material was aluminium of 94 and the remains were wood and bakelite. 3. The umber of Korean products from five companies was 33 and the one of the foreign products was 34 from companies. The physical properties have been examined by the notice of Department of Health and Social Affairs. 4. The intensity of secondary radiation was the highest in 5 : 1 grid ratio. 5. The Bucky factor increased with the increase of grid ratio. The selectivity, the grid improvement factor of grids also increased with increase of the grid ratio. However, with 6 : 1 grid ratio those factors were decreased exceptionally. In measurement of grid density with screen determiners and the beam alignment. 6. In evaluation the results were satifisfied within, 20%. 7. The value of the scale and the value of measurement were within the range of standard deviation, but the value of 103 lines were outranged from the standard deviation with all grid ratio except of 6 : 1 grid ratio.

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.85-91
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• 2018

Computed tomography, which obtains section images from reconstruction process using projection images, has been applied to various fields. The spatial resolution of the reconstructed image depends on the device used in CT system, the object, and the reconstruction process. In this paper, we investigates the effect of the number of projection images and the pixel size of the detector on the spatial resolution of the reconstructed image under the parallel beam geometry. The reconstruction program was written in Visual C++, and the matrix size of the reconstructed image was $512{\times}512$. The numerical bar phantom was constructed and the Min-Max method was introduced to evaluate the spatial resolution on the reconstructed image. When the number of projections used in reconstruction process was small, artifact like streak appeared and Min-Max was also low. The Min-Max showed upper saturation when the number of projections is increased. If the pixel size of the detector is reduced to 50% of the pixel size of the reconstructed image, the reconstructed image was perfectly recovered as the original phantom and the Min-Max decreased as increasing the detector pixel size. This study will be useful in determining the detector and the accuracy of rotation stage needed to achieve the spatial resolution required in the CT system.