• Progress in Medical Physics
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• v.13 no.3
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• pp.129-134
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• 2002

The radiosurgery is planned that prescribed dose was irradiated to tumor for obtaining expected remedial value in stereotactic radiosurgery. The planning for many irregular tumor shape requires long computation time and skilled planners. Due to the rapid development in computer power recently, many optimization methods using computer has been proposed, although the practical method is still trial and error type of plan. In this study, many beam variables were considered and many tumor shapes were assumed cylinderical ideal models. Then, beam variables that covered the target within 50％ isodose curve were searched, the result was compared and analysed. The beam variables considered were isocenter separation distance, number of isocenters and collimator size. Dose distributions obtained with these variables were analysed by dose volume histogram(DVH) and dose profile at orthogonal plane. According to the results compared, the use of more isocenters than specified isocenter dosen't improve DVH and dose profile but only increases complexity of plan. The best result of DVH and dose profile are obtainedwhen isocenter separation was 1.0-1.2 in using same number of isocenter.

• Progress in Medical Physics
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• v.7 no.1
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• pp.53-64
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• 1996

Purpose: The purposes of this paper are to develop a theoretical basis that the beam directions should be considered when the mechanical accuracy of teletherapy machine is evaluated by the star pattern test, to develop methods using asymmetric field in length to simulate beam direction for the case that beam direction does not appear on film. Method: In evaluating mechanical rotational accuracy of the gantry of teletherapy unit by the star pattern test, the direction of radiation beams was considered. A star pattern using some narrow beams was made. Density profiles at 10cm far from estimated gantry axis on the star pattern were measured using an optical densitometer. On each profile, one coordimate of a beam axis was determined. A pair of coordinates on a beam axis form an equation of the axis. Assume that a unit vector equation omitted is with same direction as radiation beam and a vector equation omitted is a vector directing to the beam axis from the estimated gantry axis. Then, a vector product equation omitted ${\times}$ equation omitted is an area vector of which the absolute value is equal to the distance from the estimated gantry axis to the beam axis. The coordinate of gantry axis was obtained by using least-square method for the area vectors relative to the average of whole area vectors. For the axis, the maximum of absolute value of area vectors would be an accuracy of the gantry rotation axis. For the evaluation of mechanical accuracies of collimator and couch axes for which beam direction could not be depicted on a star pattern test film, narrow beams asymmetric in field length was used to simulate beam direction. Result: For a star test pattern to evaluate the mechanical accuracy of rotational axes of a telectherapy machine, the result considering beam direction was different from that ignoring beam direction. For the evaluation of mechanical accuracies of collimator and couch axes by means of a star pattern test, narrow asymmetric beams could simulate beam direction. Conclusion: When a star pattern test is used to evaluate the mechanical accuracy of a teletherapy unit, beam direction must be considered or simulated, and quantitatively evaluated.

• Progress in Medical Physics
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• v.25 no.4
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• pp.288-297
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• 2014

Dynamic conformal arc therapy (DCAT) and flattening-filter-free (FFF) beams are commonly adopted for efficient conformal dose delivery in stereotactic body radiation therapy (SBRT). Off-axis geometry (OAG) may be necessary to obtain full gantry rotation without collision, which has been shown to be beneficial for peripheral targets using flattened beams. In this study dose distributions in OAG using FFF were evaluated and the effect of mechanical rotation induced uncertainty was investigated. For the lateral target, OAG evaluation, sphere targets (2, 4, and 6 cm diameter) were placed at three locations (central axis, 3 cm off-axis, and 6 cm off-axis) in a representative patient CT set. For each target, DCAT plans under the same objective were obtained for 6X, 6FFF, 10X, and 10FFF. The parameters used to evaluate the quality of the plans were homogeneity index (HI), conformality indices (CI), and beam on time (BOT). Next, the mechanical rotation induced uncertainty was evaluated using five SBRT patient plans that were randomly selected from a group of patients with laterally located tumors. For each of the five cases, a plan was generated using OAG and CAG with the same prescription and coverage. Each was replanned to account for one degree collimator/couch rotation errors during delivery. Prescription isodose coverage, CI, and lung dose were evaluated. HI and CI values for the lateral target, OAG evaluation were similar for flattened and unflattened beams; however, 6FFF provided slightly better values than 10FFF in OAG. For all plans the HI and CI were acceptable with the maximum difference between flattened and unflattend beams being 0.1. FFF beams showed better conformality than flattened beams for low doses and small targets. Variation due to rotational error for isodose coverage, CI, and lung dose was generally smaller for CAG compared to OAG, with some of these comparisons reaching statistical significance. However, the variations in dose distributions for either treatment technique were small and may not be clinically significant. FFF beams showed acceptable dose distributions in OAG. Although 10FFF provides more dramatic BOT reduction, it generally provides less favorable dosimetric indices compared to 6FFF in OAG. Mechanical uncertainty in collimator and couch rotation had an increased effect for OAG compared to CAG; however, the variations in dose distributions for either treatment technique were minimal.

• Radiation Oncology Journal
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• v.28 no.2
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• pp.99-105
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• 2010

Purpose: To compare radiation dose of the brain and lens among various conventional whole brain radiotherapy (WBRT) techniques. Materials and Methods: Treatment plans for WBRT were generated with planning computed tomography scans of 11 patients. A traditional plan with an isocenter located at the field center and a parallel anterior margin at the lateral bony canthus was generated (P1). Blocks were automatically generated with a 1 cm margin on the brain (5 mm for the lens). Subsequently, the isocenter was moved to the lateral bony canthus (P2), and the blocks were replaced into the multileaf collimator (MLC) with a 5 mm leaf width in the craniocaudal direction (P3). For each patient plan, 30 Gy was prescribed at the isocenter of P1. Dose volume histogram (DVH) parameters of the brain and lens were compared by way of a paired t-test. Results: Mean values of $D_{max}$ and $V_{105}$ of the brain in P1 were 111.9% and 23.6%, respectively. In P2 and P3, $D_{max}$ and $V_{105}$ of the brain were significantly reduced to 107.2% and 4.5~4.6%, respectively (p<0.001). The mean value of $D_{mean}$ of the lens was 3.1 Gy in P1 and 2.4~2.9 Gy in P2 and P3 (p<0.001). Conclusion: WBRT treatment plans with an isocenter located at the lateral bony canthus have dosimetric advantages for both the brain and lens without any complex method changes.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.67-67
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• 2003

It is crucial to minimize setup errors of a cancer treatment machine using a high energy and to perform precise radiation therapy. Usually, port film has been used for verifying errors. The Korea Cancer Center Hospital (KCCH) has manufactured digital electronic portal imaging device (EPID) system to verify treatment machine errors as a Quality Assurance (Q.A) tool. This EPID was consisted of a metal/fluorescent screen, 45$^{\circ}$ mirror, a camera and an image grabber and could display the portal image with near real time KIRAMS has also made the acrylic phantom that has lead line of 1mm width for ligh/radiation field congruence verification and reference points phantom for using as an isocenter on portal image. We acquired portal images of 10$\times$10cm field size with this phantom by EPID and portal film rotating treatment head by 0.3$^{\circ}$, 0.6$^{\circ}$ and 0.9$^{\circ}$. To check field size, we acquired portal images with 18$\times$18cm, 19$\times$19cm and 20$\times$20cm field size with collimator angle 0$^{\circ}$ and 0.5$^{\circ}$ individually. We have performed Flatness comparison by displaying the line intensity from EPID and film images. The 0.6$^{\circ}$ shift of collimator angle was easily observed by edge detection of irradiated field size on EPID image. To the extent of one pixel (0.76mm) difference could be detected. We also have measured field size by finding optimal threshold value, finding isocenter, finding field edge and gauging distance between isocenter and edge. This EPID system could be used as a Q.A tool for checking field size, light/radiation congruence and flatness with a developed video based EPID.

• Journal of Radiation Industry
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• v.17 no.1
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• pp.1-9
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• 2023

Since a large amount of radioactive waste is expected to be generated due to permanent shutdown of many nuclear power plants, it is necessary to prepare efficient management methods for radioactive waste. Therefore, there is a need for a based study to apply the In-Situ gamma spectrometry, which can simplify the measurement procedure. The purpose of this study is to analyze research cases of In-Situ gamma spectrometry and to analyze the sensitivity of measurement according to influencing factors on In-Situ gamma spectrometry. Research cases of five institutions, including the CERN and the Imperial College Reactor Centre (ICRC), were selected as the institutions to be investigated. Research on the In-Situ gamma spectrometry was conducted on the satisfaction of the acceptance criteria for radioactive waste and the analysis of residual radioactivity in the site. In-Situ Objective Counting System (ISOCS) was used as a major measuring device. Sampling and computer code were used to verify the analysis results. For evaluation of measuring sensitivity according to influencing factors on In-Situ gamma spectrometry, the thickness of the measurement target, the distance between the detector and the target, the angle of the collimator, and the contamination location were performed using ISOCS's Geometry Composer. In every case, based on 122 keV, the efficiency decreased as the energy increased in the high energy region, and the efficiency decreased as the energy decreased in the low energy region. As the target thickness increased, the efficiency decreased, and as the distance between target and detector increased, the efficiency decreased. As the distance between contamination and detector increased, the efficiency decreased, and as the angle of the collimator increased, the measurement efficiency increased. However, when simulating the measurement situation using Geometry Composer, the background is not considered, and the probability of incident in the background increases as the angle increases, so further research needs to be conducted in consideration of these. This study can be utilized when applying the In-Situ gamma spectrometry of radioactive waste clearance in the future.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.6
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• pp.793-799
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• 2014

EO GRD(Ground Resolved Distance) resolution of airborne EO/IR(Electro-Optical/Infrared) sensor is a critical factor in test and evaluation for EO sensor performance. We propose the laboratory measurement set-up for EO GRD by constructing optical collimator which includes integrated sphere, blackbody, equivalent 3-bar target and 6 DOF motion simulator. GRD is measured in the photographic imagery of bar targets by 3 different distances for 3 EO/IR sensors and the measured results were analyzed statistically. We found that at least 7 sheets of imagery are needed in order to obtain meaningful EO GRD. The result of statistical analysis shows that the distribution of the measured GRD is nearly symmetric about the average GRD, and the better imagery ratio above the average GRD is about 40~70%. Also from the best GRD analysis, it is estimated that the design goal for EO GRD should be 30% superior to the required GRD.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.10
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• pp.98-103
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• 2005

The Flight Model of MAC (Medium-sized Aperture Camera), a 2.5m GSD class earth observation camera has been aligned and assembled. Topics discussed in this paper include the ground MTF performance of the MAC system, and the alignment of the focal plane assembly. MTF was measured by a knife-edge scanning technique, and a 450 mm diameter Cassegrain collimator with diffraction-limited performance was made and used for the MTF measurements. System MTF was used as the figure-of-merit to find the best focus of the focal plane assembly.

• Korean Journal of Optics and Photonics
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• v.7 no.3
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• pp.191-195
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• 1996

A optical system of a movile LIDAR is designed for air pollution research. After the inverse Cassegrain type collimator, the laser beam falls on the mirror which serve for coinciding optical axis of laser beam and the receiving telescope. Then, it is directed into the atmosphere and back scattered radiation back to the receiving telescope by the scanning mirror. The unit of scanning mirror allows to rotate the mirror along the altitude 0$^{\circ}$~60$^{\circ}$, and the azimuth 0$^{\circ}$~360$^{\circ}$. The scanning mirror is not connected with the receiving telescope but placed on the roof of the mobile. The received beam is spatial filtered by a spatial filter and collimated by a fabric lens. Thereafter, the beam is devided into 2 channel for registration by a beam splitter. Each laser beam is transformed into an electrical signal by means of the photomultifier and then processed to be analyzed.

• Imaging Science in Dentistry
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• v.31 no.3
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• pp.153-158
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• 2001

Purpose : To determine the head position that the superior border of the mandibular canal as well as mental foramen can be more clearly visualized in panoramic radiography Materials and Methods : Ten dry mandibles were radiographed bilaterally using PM 2002 CC panoramic machine. A 20 mm thick aluminium filter was added to the slit collimator to obtain radiographs with acceptable density. The specimens were tilted by 2, 4, 6, 8, and 10 degrees downward with and without radiopaque markers. Radiopaque markers were inserted into the mandibular canals and the mental canals of each side of the specimens to serve as reference image when assessing the radiographs. The visibility of the mandibular canal and the mental foramen was estimated by 4 observers on all radiographs. The obtained results were analyzed statistically. Results: Mandibular canals were significantly more clearly visible in the radiographs with 4 and 6 degree downward position on both sides (P<0.05). Mental foramens were significantly more clearly visible in the radiographs with 4, 6, and 8 degree downward on right side and 6 degree downward on left side (P<0.05). There was not significant difference between right and left sides. Conclusion: Panoramic radiographs with 4 to 6 degree downward tilting could be valuable in locating the mandibular canal as well as the mental foramen.