• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.71-74
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• 2002

Currently small and accurate dosimeters are on the rise. In this study, the feasibility and energy dependency of the electret dosimeter that made of PET (polyethylene terephtalate) were observed by irradiating 4, 6, 15 MV photon beams from the clinical linear accelerator to develop a dosimeter for the clinical field. $10{\times}10cm$ field size of the photon beams were irradiated to the electret dosimeter where the 2.5 cm depth in the polystylene phantom from 100 cm SSD, while 300 DCV was applied to the electret dosimeter. The result showed that the absorbed dose was proportional to the charge linearly, and the volume of a dosimeter could be reduced and the signals were high enough. According to this study, it was found that the polymer electret detector could be produced as a large quantity with a small cost and showed the feasibility of a realtime measurement.

• Radiation Oncology Journal
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• v.23 no.3
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• pp.186-193
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• 2005

Purpose: To improve the management of a medical linear accelerator, the records of operational failures of a Varian CL2l00C over a ten year period were retrospectively analyzed. Materials and Methods: The failures were classified according to the involved functional subunits, with each class rated Into one of three levels depending on the operational conditions. The relationships between the failure rate and working ratio and between the failure rate and outside temperature were investigated. In addition, the average life time of the main part and the operating efficiency over the last 4 years were analyzed. Results: Among the recorded failures (total 587 failures), the most frequent failure was observed in the parts related with the collimation system, including the monitor chamber, which accounted for $20\%$ of all failures. With regard to the operational conditions, 2nd level of failures, which temporally interrupted treatments, were the most frequent. Third level of failures, which interrupted treatment for more than several hours, were mostly caused by the accelerating subunit. The number of failures was increased with number of treatments and operating time. The average life-times of the Klystron and Thyratron became shorter as the working ratio increased, and were 42 and $83\%$ of the expected values, respectively. The operating efficiency was maintained at $95\%$ or higher, but this value slightly decreased. There was no significant correlation between the number of failures and the outside temperature. Conclusion: The maintenance of detailed equipment problems and failures records over a long period of time can provide good knowledge of equipment function as well as the capability of predicting future failure. Wore rigorous equipment maintenance Is required for old medical linear accelerators for the advanced avoidance of serious failure and to improve the qualify of patient treatment.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1370_1372
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• 2009

A conventional linear accelerator system requires a flat-topped pulse with less than $\pm$ 0.5% ripple to meet the beam energy spread requirements and to improve pulse efficiency of RF systems. A a line-type pulsed modulator is widely used in pulsed power circuits for applications such as accelerators, radar, medical radiation, or ionization systems. The high-voltage pulse generator system with an output voltage of 284 kV, a pulse width of $10{\mu}s$, and a rise time of $0.84{\mu}s$ has been designed and fabricated to drive a klystron which has 30-MW peak and 60-kW average RF output power. The high-voltage test was performed using the klystron load. This thesis describes the design and test results of high-power pulse generator system for industrial accelerator application. The experimental results were analyzed and compared with the design.

• 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.

• The Journal of Korean Society for Radiation Therapy
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• v.6 no.1
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• pp.89-93
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• 1994

Authors have measured virtual source distance of electron beam from CL/1800 medical linear accelerator, with newly designed method. Beam scanning was performed with the direction of beam axis in the air. Compared results between this study and well established in phantom measurement shows good agreement with in experimental error. And we have found that build-up cap plays very important role in air measurement because of charge build up. The method of in-air measurement of virtual source distance is very easy to set-up and generate accurate results.

• Journal of Biomedical Engineering Research
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• v.13 no.1
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• pp.19-24
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• 1992

Lineacgrams are diagnostic films taken using X-ray from the linear accelerator with the patient in the treatment position to assure that the treatment is being delivered in accordance with the treatment prescription. But the image quality of the lineacgram is so bad because of the high X-ray energy. This paper presents a new algorithm that enhances the image of lineacgram. Thls algorithm calculates optimal threshold value which is used for segmentation of lineacgram using co-occurrence matrix and enhances the image Inside and outside treatment area preserving treatments boundary.

• Progress in Medical Physics
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• v.14 no.4
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• pp.225-233
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• 2003

The goal of a radiation treatment plan is to deliver a homogeneous dose to a target with minimal irradiation of the adjacent normal tissues. Dose uniformity is especially important for stereotactic radiosurgery using a linear accelerator. The dose uniformity and high dose delivery of a single spherical dose distribution exceed 70％. This also results with a similar stereotactic radiosurgical plan using a Gamma Knife. The dose distribution produced in a stereotactic radiosurgical plan using a Gamma Knife and Linear accelerator is spherical, and the application of the sphere packing arrangement in a real radiosurgical plan requires much time and skill. In this study, we found a characteristic of dose distribution with transformation of beam parameters that must be considered in a radiosurgical plan for effective radiosurgery. First, we assumed a cylinder type tumor model and a cube type tumor model. Secondly, the results of the tumor models were compared and analyzed with dose profiles and DVH_(Dose Volume Histogram) representative dose distribution. We found the optimal composition of beam parameters_(i.e. collimator size, number of isocenter, gap of isocenters etc.), which allowed the tumor models to be involved in the isodose curve at a high level. In conclusion, the characteristics found in this study are helpful for improving the effectiveness and speed of a radiosurgical plan for stereotactic radiosurgery.

• Progress in Medical Physics
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• v.29 no.3
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• pp.92-100
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• 2018

The manufacturer of a linear accelerator (LINAC) has reported that the target melting phenomenon could be caused by a non-recommended output setting and the excessive use of monitor unit (MU) with intensity-modulated radiation therapy (IMRT). Due to these reasons, we observed an unexpected beam interruption during the treatment of a patient in our institution. The target status was inspected and a replacement of the target was determined. After the target replacement, the beam profile was adjusted to the machine commissioning beam data, and the absolute doses-to-water for 6 MV and 10 MV photon beams were calibrated according to American Association of Physicists in Medicine (AAPM) Task Group (TG)-51 protocol. To verify the beam data after target replacement, the beam flatness, symmetry, output factor, and percent depth dose (PDD) were measured and compared with the commissioning data. The difference between the referenced and measured data for flatness and symmetry exhibited a coincidence within 0.3% for both 6 MV and 10 MV, and the difference of the PDD at 10 cm depth ($PDD_{10}$) was also within 0.3% for both photon energies. Also, patient-specific quality assurances (QAs) were performed with gamma analysis using a 2-D diode and ion chamber array detector for eight patients. The average gamma passing rates for all patients for the relative dose distribution was $99.1%{\pm}1.0%$, and those for absolute dose distribution was $97.2%{\pm}2.7%$, which means the gamma analysis results were all clinically acceptable. In this study, we recommend that the beam characteristics, such as beam profile, depth dose, and output factors, should be examined. Further, patient-specific QAs should be performed to verify the changes in the overall beam delivery system when a target replacement is inevitable; although it is more important to check the beam output in a daily routine.

• Journal of radiological science and technology
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• v.40 no.2
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• pp.297-302
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• 2017

In this study, the generation of photoneutrons between the 10 MV FF mode and the FFF mode was evaluated and the amount of photoneutrons generated by the 10 MV and 15 MV energy changes in the FFF mode was evaluated. The generated neutrons were evaluated at 13 measurement points and the KTEPC was used to collect the generated neutrons. 10 MV FF mode was measured at 10 MV FF mode and FFF mode at all measurement points. In the superior direction, 0.455mSv and 0.152mSv were the largest, and more than 33% optical neutron was generated in FF. 10 MV in FFF mode, 15 MV in 15 MV, and 0.402 mSv in the direction of Superior, and 6.9% in the direction.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.411-414
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• 2002

The CdTe semiconductor detector has a higher detection efficiency for x-rays and $\square$amma rays and a wider energy band gap compared with Si and Ge semiconductor detectors. Therefore, the size of the detector element can be made small, and can be operated at room temperature. The interaction between a CdTe detector and incident x-rays is mainly photoelectric absorption in the photon energy range of up to 100 keV. In this energy range, Compton effects are almost negligible. We have developed a 256 channel CdTe array detector system for monochromatic x-ray CT using synchrotron radiation. The CdTe array detector system, the element size of which is 1.98 mm (h) x 1.98 mm (w) x 0.5 mm (t), was operated in photon counting mode. In order to improve the spatial resolution, we tilted the CdTe array detector against the incident parallel monochromatic x-ray beam. The experiments were performed at the BL20B2 experimental hutch in SPring-8. The energy of incident monochromatic x-rays was set at 55 keV. Phantom measurements were performed at the detector angle of 0, 30 and 45 degrees against the incident parallel monochromatic x-rays. The linear attenuation coefficients were calculated from the reconstructed CT images. By increasing the detector angle, the spatial resolutions were improved. There was no significant difference between the linear attenuation coefficients which were corrected by the detector angle. It was found that this method was useful for improving the spatial resolution in a parallel monochromatic x-ray CT system.