• Journal of radiological science and technology
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• v.35 no.4
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• pp.335-343
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• 2012

Intensity-modulated radiotherapy(IMRT) have the ability to provide better dose conformity and sparing of critical normal tissues than three-dimensional radiotherapy(3DCRT). Especially, with the benefit of health insurance in 2011, its use now increasingly in many modern radiotherapy departments. Also the use of linear accelerator with high-energy photon beams over 10 MV is increasing. As is well known, these linacs have the capacity to produce photonueutrons due to photonuclear reactions in materials with a large atomic number such as the target, flattening filters, collimators, and multi-leaf collimators(MLC). MLC-based IMRT treatments increase the monitor units and the probability of production of photoneutrons from photon-induced nuclear reactions. The purpose of this study is to quantitatively evaluate the dose of photoneutrons produced from 3DCRT and IMRT technique for Rando phantom in cervical cancer. We performed the treatment plans with 3DCRT and IMRT technique using Rando phantom for treatment of cervical cancer. An Rando phantom placed on the couch in the supine position was irradiated using 15 MV photon beams. Optically stimulated luminescence dosimeters(OSLD) were attached to 4 different locations (abdomen, chest, head and neck, eyes) and from center of field size and measured 5 times each of locations. Measured neutron dose from IMRT technique increased by 9.0, 8.6, 8.8, and 14 times than 3DCRT technique for abdomen, chest, head and neck, and eyes, respectively. When using IMRT with 15 MV photonbeams, the photoneutrons contributed a significant portion on out-of-field. It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, it is need to provide the additional safe shielding on a linear accelerator and should therefore reduce the out-of-field dose.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.2
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• pp.123-129
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• 2010

Purpose: The purpose of this study was to evaluate dosimetric characteristics of Optically stimulated luminescent dosimeters (OSLD) for dosimetry Materials and Methods: InLight/OSL $NanoDot^{TM}$ dosimeters was used including $Inlight^{TM}MicroStar$ Reader, Solid Water Phantom, and Linear accelerator ($TRYLOGY^{(R)}$) OSLDs were placed at a Dmax in a solid water phantom and were irradiated with 100 cGy of 6 MV X-rays. Most irradiations were carried out using an SSD set up 100 cm, $10{\times}10\;cm^2$ field and 300 MU/min. The time dependence were measured at 10 minute intervals. The dose dependence were measured from 50 cGy to 600 cGy. The energy dependence was measured for nominal photon beam energies of 6, 15 MV and electron beam energies of 4-20 MeV. The dose rate dependence were also measured for dose rates of 100-1,000 MU/min. Finally, the PDD was measured by OSLDs and Ion-chamber. Results: The reproducibility of OSLD according to the Time flow was evaluated within ${\pm}2.5%$. The result of Linearity of OSLD, the dose was increased linearly up to about the 300 cGy and increased supralinearly above the 300 cGy. Energy and dose rate dependence of the response of OSL detectors were evaluated within ${\pm}2%$ and ${\pm}3%$. $PDD_{10}$ and PDD20 which were measured by OSLD was 66.7%, 38.4% and $PDD_{10}$ and $PDD_{20}$ which were measured by Ion-chamber was 66.6%, 38.3% Conclusion: As a result of analyzing characteration of OSLD, OSLD was evaluated within ${\pm}3%$ according to the change of the time, enregy and dose rate. The $PDD_{10}$ and $PDD_{20}$ are measured by OSLD and ion-chamber were evaluated within 0.3%. The OSL response is linear with a dose in the range 50~300 cGy. It was possible to repeat measurement many times and progress of the measurement of reading is easy. So the stability of the system and linear dose response relationship make it a good for dosimetry.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.251-259
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• 1996

Two-Photon Fluorescence (TPF) experiment measures temporal width of an amplified short laser pulse which has passed through a four-pass Nd: glass amplifier, after selecting a single pulse from pulse train Q-switched and mode-locked(QSML) in Nd:YLF master oscillator. Determination of pulsewidth and pulseshape was also made with detection of autocorrelation trace of CW mode-locked pulse train by using noncollinear type I Second Harmonic Generation (SHG) method. The observed TPF track showed various patterns, depending on pulse-selecting position in QSML pulse train. That is, autocorrelation of a pulse extracted at front of the train displayed smooth pulse shape, while one from the trailing part of the train created many sharp spikes and substructure in the pulse. By TPF method, pulsewidth was measured to be 44.4 ps with contrast ratio of 2.86 which enabled us to find out energy fraction of a pulse to total energy, (sum of pulse and background); we obtain the value of 0.62. Pulsewidth of 46.6ps was also acquired in another SHG experiment with the help of only mode-locked pulse train. On the other hand, we confirmed that shape of the pulse is close to $sech^2$ one as a result of fitting the SHG autocorrelation signal with various functions. With simulation using this $sech^2$ type of pulse, pulsewidth reduction of the beam, having passed through four-pass amplifier, was also verified.

• Progress in Medical Physics
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• v.11 no.2
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• pp.91-99
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• 2000

This is a preliminary study for developing the method of the dose reconstruction in the patients, irradiated by mega-voltage photon beams from the linear accelerator, using the transit dose distributions. In this study we present the method of three-dimensional dose reconstruction and evaluate the method by computer simulation. To acquire the dose distributions in the patients (or phantoms) we first calculate the differences between the doses at the arbitrary points in the patients and the doses at the corresponding points where the transit doses are measured. Then, we can get the dose in the patients from the measured transit dose and the calculated value of the difference. The dose differences are calculated by applying the inverse square law and using the linear attenuation coefficient. The scatter to primary dose ratios, which are calculated by the Monte Carlo program using the CT data of the patient (or phantoms), are also used in the calculations. For the evaluation of this method we used various kinds of homogeneous and inhomogeneous phantoms and calculated the transit dose distributions with the Monte Carlo program. From the distributions we reconstructed the dose distributions in the phantom. We used mono-energy Photon beam of 1.5MeV and Monte Carlo program EGS4. The comparison between the dose distributions reconstructed using the method and the distributions calculated by the Monte Carlo program was done. They agreed within errors of -4%∼+2%. This method can be used to predict the dose distributions in the patient

• Journal of the Korean Society of Radiology
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• v.9 no.4
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• pp.239-247
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• 2015

It should be accurate dose calculation to increase the efficiency of radiation therapy, and it is priority to figure out the beam characteristics for this purpose. The target and primary collimator in head components of the linear accelerator have the greatest influence on determining the beam characteristics which is caused by backscatter and it is the factor to consider the shielding structures and equipment management. In this study, we made modeling of the linear accelerator through the Geant4 Monte Carlo simulation and investigated backscatter according to the change of the size and shape in head components. For the scattered electrons, it showed the greatest number of distributions inside of the inner radius at primary collimator. But, for the scattered photons which have the high energy, it was mostly located outside of the inner radius at primary collimator. Scattered positrons showed a small occurrence in about 0.03%. According to the change of the inner radius at primary collimator, it was great changes in the inside of inner radius for all three scattered particles. According to the change of the outer radius at primary collimator, it was shown some considerable effects from more than 60 mm outer radius. It was no significant effect according to the change of target thickness. In this study, we found that backscatter should be considered, and figured out that geometric size and shape of the peripheral components are the factors that influences the backscatter effect.

• Progress in Medical Physics
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• v.16 no.3
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• pp.116-124
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• 2005

Absorbed dose dosimetry protocols of high energy photon and electron beams, which are widely used and based on an air kerma calibration factors, have somewhat complex formalism and limitations for improving dosimetric accuracy due to uncertainty of the physical parameters used. Recently the IAEA and the AAPM published the absorbed dose to water-based dosimetry protocol. In this work web-based dose calibration program for IAEA TRS-398 and AAPM TG-51 protocols were developed. This program developed using the Visual C$\#$ language can be used in the internet. User selectable dosimetry protocol on the web allows the absorbed dose to water data of the two protocols at a reference point to be easily compared, and enables to conveniently manage and understand the current status of the dosimetry calibration performed at participating institutions in korea. This program and the resultant database from the web-based calibration can be useful in developing new dosimetry protocols in Korea.

• Journal of the Korean Society of Radiology
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• v.13 no.4
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• pp.523-530
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• 2019

The purpose of this study was to obtain the K-edge images using a spectral CT system based on a photon-counting detector and implement the 3D fusion imaging using the conventional and spectral CT images. Also, we evaluated the clinical feasibility of the 3D fusion images though the quantitative analysis of image quality. A spectral CT system based on a CdTe photon-counting detector was used to obtain K-edge images. A pork phantom was manufactured with the six tubes including diluted iodine and gadolinium solutions. The K-edge images were obtained by the low-energy thresholds of 35 and 52 keV for iodine and gadolinium imaging with the X-ray spectrum, which was generated at a tube voltage of 100 kVp with a tube current of $500{\mu}A$. We implemented 3D fusion imaging by combining the iodine and gadolinium K-edge images with the conventional CT images. The results showed that the CNRs of the 3D fusion images were 6.76-14.9 times higher than those of the conventional CT images. Also, the 3D fusion images was able to provide the maps of target materials. Therefore, the technique proposed in this study can improve the quality of CT images and the diagnostic efficiency through the additional information of target materials.

• Journal of the Korean Society of Radiology
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• v.10 no.2
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• pp.125-131
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• 2016

Radiation therapy is usually using linear accelerator and used X-ray energy is also getting higher. Recently linear accelerators has been developed 3F mode and tracking jaw technology and that was applied for patient therapy. This study aims at measuring photoneutrons depending on the use of 3F and tracking jaw system when radiation is irradiated using a linear accelerator. The generation of photoneutrons of 3F system was 70% smaller than 2F system and that of tracking jaw system was 83% higher than static jaw system. Photoneutron value is relatively low. However, it must be minimized for Photoneutron exposure during radiation therapy.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.405-405
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• 2016

CIGS 박막 태양전지에서 완충층으로 사용되는 ZnS는 단파장 영역에서 높은 투과도와 CIGS 계면과의 좋은 접착을 가지고 친환경적이며 3.74eV의 에너지 밴드갭을 가지고 있기 때문에 CdS를 사용했을 때 보다 더 넓은 에너지 영역의 광자를 p-n 접합 경계 영역으로 통과 시킬 수 있고 Cd-free 물질이라는 점에서 기존의 CdS 완충층의 대체 물질로 각광 받고 있다. 본 연구에서는 CIGS 박막에 화학습식공정 방법을 이용하여 최적화된 ZnS 박막의 증착 조건을 찾기 위해 실험 변수인 시약의 농도, 실험온도, 열처리 조건 등의 다양한 변화를 통해 실험을 진행하였고, 박막의 갈라짐과 pin-hole 현상을 개선하고 균일한 막을 제조하기 위해 구연산 나트륨 농도에 따른 ZnS 박막의 특성을 연구하였다. 본 실험 결과로서 실험변수인 황산아연의 농도 0.15M, 암모니아는 0.3M, 티오요소 1M, 공정 온도 $80^{\circ}C$의 최적화 된 조건에서 가장 좋은 품질의 ZnS 박막을 제조하였지만, ZnS 박막의 열처리 후 산소의 양이 줄어감에 따라 박막의 표면이 갈라지고 pin-hole 현상이 발생하는 것을 확인할 수 있었다. 박막의 품질을 개선하기 위해 구연산 나트륨을 첨가하여 실험한 결과 구연산 나트륨의 0.05M의 농도에서는 박막 표면에 90nm의 갈라짐의 크기와 pin-hole 현상이 남아있는 것을 확인하였고, 농도가 높아질수록 점차 크기가 줄어들면서 0.4M에서는 갈라짐이 거의 없는 표면과 pin-hole 현상도 없어지는 것을 확인하였고, 약 144nm의 박막 두께와 3.8eV의 에너지 밴드갭을 가지고, 약 81%의 높은 광투과율을 갖는 고품질의 ZnS 박막을 제작할 수 있었다.

• Journal of Energy Engineering
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• v.13 no.2
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• pp.93-100
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• 2004

The smear media possible to sampling and radiation detection was prepared and evaluated for the surface contamination using indirect method. The films were made by impregnating Cerium Activated Yttrium Silicate (CAYS) in a polysulfone membrane. The membranes used solution as a dimethylformamide (DMF) and methylene chloride (MC), polysulfone as a polymer matrix and CAYS as a inorganic scintillator. The proximity membranes were prepared with single- and double-layered structure. The solidified methods were immersion to the nonsolvent bath such at water and ethanol and solvent evaporation. The measurement of the photon produced by interaction with radiation and inorganic scintillator used a photomultiflier tube (PMT), amplifier, and counter. In the comparison with the low background alpha/beta counter, the counter rate using inorganic scintillator proximity membrane for the $\^$14/C surface contamination was about 50%. Also. the $^3$H counting results revealed that the prepared membranes were efficient to monitor the surface contaminated with the low energy be-ray emitter nuclides.