• Progress in Medical Physics
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• v.10 no.2
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• pp.89-94
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• 1999

We developed a sterotactic radiosurgery system which is comprised of 1) collimators with small circular aperture, 2) an angiographic target localizer, 3) a target localizer used for alignment of planned target position with isocenter of treatment machine, and 4) a treatment planning system named LinaPel. In this study, we performed a series of treatment simulations to specify and analyze geometrical errors contained our in-house radiosurgery system. As results, 1) using Geometrical Phantom(Radionics,USA), the accuracy of target localization by LinaPel was determined as Avg. =(equation omitted) the accuracy of mechanical isocenter was found out to be 0.6 $\pm$ 0.2 mm, 3) the positional difference of target localization which determined by CT and angiography was 0.8 mm, and their size difference was 1.5 mm, and 4) the positional error during whole treatment was found out to be 0.9 $\pm$ 0.3 mm. With these results, we concluded that our in-house radiosurgery system can be used clinically. However, these range of accuracies need periodical quality assurance strongly.

• Journal of radiological science and technology
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• v.41 no.3
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• pp.249-254
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• 2018

In this study, we evaluated the DAP(Dose Area Product) reduction effect of the newly developed IRIS collimator by measuring the DAP of the Rectangle collimator and the IRIS collimator depending on the field, SID(Source to Image recpetor Distance) change, and AEC mode use. The results were as follows. The IRIS collimator decreased DAP by 34.91, 29.33, and 29.04%, respectively, compared to the Rectangle collimator when the field was increased to $8{\times}8$, $12{\times}12$, $16{\times}16inch$. And also, when the SID was increased to 100, 120 and 140 cm, the IRIS collimator decreased DAP by 10.73, 33.68 and 46.22%, respectively, compared to the Rectangle collimator. In AEC mode and none-AEC mode, DAP in IRIS collimator was reduced by 32.71 and 21.69%, respectively, compared with the Rectangle type. The IRIS collimator can reduce DAP by 29.62% on average compared to Rectangle type, which is statistically significant. These results suggest that the newly developed IRIS collimator can be used in medical field to alleviate radiation exposure.

• Progress in Medical Physics
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• v.6 no.2
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• pp.13-19
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• 1995

The behavior of the correction factor associated with the collimator opening(head-scatter factor) were investigated for the 6MV x-ray beams of medical linear accelerator. The primary photon fluence was measured in air quasi-small fied size. Consideration in this study was given to the effect of head scatter factor with quasi-small fied size, the upper and lower collimator jaw scatter collection factors of quasi-small field (4-10cm) were measured with ion chamber. In general, the wedge factors which are used clinical practics are ignored of dependency on field sizes and depth. In wedge factors for each wedge filter were measured at various depth by using 6MV X-ray. In this present we inverstigated systematically the depth and field sizes dependency to determine the absorbed dose more accurately. Head scatter(upper-lower collimator jaw)appears to be (1) a small effect, less than 5％ over the range of clinical field sizes (2) generated primarily at the flattening filter and therefored influenced most by the upper collimator setting.

• Progress in Medical Physics
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• v.15 no.1
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• pp.17-22
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• 2004

Multileaf collimator (MLC) is now rapidly replacing the lead ahoy block to shape the radiation treatment field. In addition to its defect of rectangular field shaping and increased penumbra width, it has another possible problem, and that is of radiation transmission between leaves, which needs to be maintained at as low a level as is permissible. The authors measured and analyzed the inter-leaf and cross-leaf transmissions of MLC by Varian Associates Inc, before its clinical application. The inter-leaf and cross-leaf transmissions were calculated by comparing the measured point doses in the polystyrene phantom in the open field and in a total closure of MLC. The beam profile of the inter-leaf and cross-leaf transmissions were depicted by using a water phantom. A photon beam of 6 MV was used in the measurement. The inter-leaf transmission was 1.63∼1.67%, indicating that the shielding effect of MLC is excellent. However, the cross-leaf transmission in the central area was 18.4∼18.7% and this is well over the clinically acceptable limitation of 5%. The beam profile of cross-leaf transmission displayed 80∼90% transmission near the field edge, so that the cross-leaf transmission was 14∼17% in this area. The multileaf collimator has an excellent shi디ding effect and the inter-leaf transmission is negligible so that it can be used in clinic as a good replacement of the conventional lead alloy block. However, care must be taken to avoid the cross-leaf transmission in the radiation field.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.6 s.312
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• pp.68-75
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• 2006

During cancer therapy by using high energy radiation, it is possible to improve the radiation therapy efficiency by performing a precise radiation therapy after verification of generated setup errors. In this paper, the video based electronic portal imaging device (EPID) which could display the portal image with near real time was developed to verify treatment position errors in radiation therapy instead of an analog typed portal film. This EPID system for applying QA tool of radiation therapy machine was consisted of a metal/fluorescent screen, $45^{\circ}$mirror, camera and image grabber. Radiation field verification has been performed to check quality assurance of the treatment machine itself by using this EPID system. The radiation field error was easily observed by edge detection of irradiated field size on EPID image when $0.6^{\circ}$ shift of collimator angle was generated. So, this implemented EPID system could be used as a radiation QA tool.

• Progress in Medical Physics
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• v.13 no.2
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• pp.90-97
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• 2002

The simulator which has a identical geometry with radiotherapy equipments, is a essential equipment to accomplish optimized radiotherapy plan through simulation by using diagnostic low energy X-ray. A Radiotherapy simulator has a combined technology from the therapeutic and diagnostic radiology and needs a periodical test for mechanical and optical properties, X-ray generator, image intensifier of simulator to keep the proper maintenance and radiation safety. Hence, tests were done and classified as i) mechanical and optical parameter for the gantry, collimator, and couch ii) key performance of the X-ray generator such as a kVp, mAs, and timer iii) performance of the image intensifier such as a resolution and contrast for three kinds of simulator, common use in clinic. The above result of tests will be applied to the acceptance test and periodical quality assurance procedure.

• Journal of the Korean Society of Radiology
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• v.5 no.3
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• pp.121-125
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• 2011

This study was intended to evaluate the surface dose and depth dose of according to the distance of the treatment room wall. High energy photon beams from linear accelerators produce large scattered radiation by various components of the treatment head, collimator and walls or objects in the treatment room including the patient. The scattered radiation measured by thermoluminescence dosimeter(TLD). Linear accelerators rotation center of the four walls(X) distance was measured to be 236, 272, 303, and 337 cm. The result of 100 cGy and 200 cGy of 6 MV photon irradiation, surface dose was 0.49, 0.83 mSv at 236 cm of the shortest distance to the wall, In 272 cm 0.41, 0.53 mSv, 303 cm in the 0.28, 0.57 mSv, and 337 cm distance from the wall in the 0.33, 0.76 mSv surface dose respectively. There was remarkable difference in the surface dose among the treatment room wall distance. The results of useful data in relation to stochastic effect for radiation therapy patients.

• Progress in Medical Physics
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• v.12 no.2
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• pp.133-140
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• 2001

The dose calculations for blocked fields were studied. The shielding block correction factors(K$_{b}$) as a function of collimator and blocked field size(r$_{c}$ and r$_{b}$) were measured. A simplified $K_{b}$ as a function of $A_{r}$ (the A/P ratio of r$_{b}$ to r$_{c}$) was determined by measured data and a fitting function for $K_{b}$ was obtained. We found that the corrections of $K_{b}$ for blocked fields in MU(monitor units) calculations need not take into account in common case of $A_{r}$ \ulcorner1 but the errors will be 3.5% in particular case such as $A_{r}$ = 0.5. These results imply that the shielding block correction for blocked fields in clinical dose calculations must be considered.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.944-945
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• 2016

Gamma-ray Detector for gamma-ray imaging device is composed of a shielding body for shielding gamma-rays incident from the radiation source. Distribution of the gamma ray can be represented by the distribution information on the direction in which the detecting section and the signal through the incident hole of collimator. The role of the shield is important because all signals should be treated as noise except for the signal from the incident hole.In this paper In this paper, we have produced a compact, lightweight and Collimator shield by changing the structure and physical properties with respect to the collimator and shielding of lead-based gamma-ray detectors. And we analyzed the shielding effectiveness relative to the incident gamma ray sphere measured signal value through the gamma irradiation test facility. The results confirmed that the production and Collimator shielding the imaging device Implementing more efficient to implement.

• Journal of Aerospace System Engineering
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• v.13 no.4
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• pp.26-36
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• 2019

The precise alignment between optical components is required in high-resolution earth observation satellites. However, the misalignment of optical components occurs due to external factors such as severe satellite launch environment and space environment. A satellite optical system with a focus mechanism is required to compensate for the image quality degraded by these misalignments. This study designed, fabricated, aligned precisely, and carried out a performance tests for the image quality of the system. The satellite optical camera performance tests were carried out to check the image quality change by operating the focus mechanism and to analyze the satellite optical system MTF by photographing USAF target using the autocollimator. According to the experimental results, the misalignments can be compensated sufficiently with the focus mechanism. Finally the basic data for re-focusing algorithm of the optical system was obtained through this study.