• Progress in Medical Physics
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• v.14 no.1
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• pp.28-33
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• 2003

The aim of the study was to assess the isocenter deviation between multiple arcs and conformal beams in frameless FSRT. Forty seven patients received single isocenter radiosurgery or therapy (SRS/T) using available framelss FSRT system from Aug. 1997 to Dec. 2m. In choosing multiple arc FSRT or conformal FSRT, we had considered one of two techniques with respect to tumor size and tumor shape. In multiple arc FSRT, the average and standard deviation (SD) of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.2 mm (SD 0.2) and 0.3 mm (SD 0.2 mm)in the lateral (x), anterior-posterior (y) and cranio-caudal directions (z). In conformal FSRT, the average deviation and SD of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.3 mm(0.2 mm) and 0.4 mm (SD 0.2 mm) in the x, y and z directions. The average spacial deviation ($\Delta$r) was 0.41 mm and 0.54 mm in multiple arcs and conformal beams, respectively. The isocenter deviation using frameless FSRT system was similar value between multiple arcs and conformal beams. In practice, we believed we can select the appropriate treatment technique according to tumor shape and size.

• Progress in Medical Physics
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• v.13 no.3
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• pp.135-138
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• 2002

Fractionated stereotactic radiosurguy (FSRS) requires precise and reproducible patient set up. For these reasons non-invasive mask fixation methods have been used in Linac based FSRS. In this study, we measured and assessed the isocenter reproducibility using a commercial head mask fixation system based on thermoplastic materials. For the verification and the measurement of isocenter deviation a special acrylic brain phantom was designed. The designed phantom has 22 vertical rods and each rod has different lengths. At the end of the 8 rods, the monochromic film is attached and irradiated due to planned target position. Deviations of isocenter were measured separately for each direction. The mean deviation showed 0.4 mm in longitudinal direction, 0.1 mm in the lateral direction, 0.1 mm in the anterior-posterior direction of the treatment couch. The data demonstrates the high accuracy and reproducibility. This study reinforces previous literature published.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.195-197
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• 2010

본 논문은 기존 평행좌표를 이용하는 얼굴 영상 대신 극좌표계 변환을 이용한 얼굴 영상을 이용하여 회전에 강인한 얼굴인식 방법을 제안한다. 극좌표계 변환 방법은 얼굴의 중심부분의 한 점을 극으로 삼아 이 점을 기준으로 360도 각 방향으로 일정 길이만큼 얼굴 영상을 샘플링 하여 새로운 얼굴 영상을 제작하는 방법이다. 이 극좌표계 변환 방법을 이용해 재구성된 영상에 대해 회귀( regression )문제 해결을 위해 변형된 LDA인 LDAr(LDA for regression)을 이용하여 얼굴의 중심부분의한 점인 극을 중심으로 임의의 각도로 회전된 영상의 회전 정도를 추정하여 이를 정규화 시키는 방법을 통해 얼굴 인식의 인식률을 향상시키고자 한다. LDAr은 LDA의 기본개념인 각 클래스 간 떨어진 정도를 최대화하는 것이 목적으로 클래스간 분산과 클래스내 분산의 비율을 최대화 하는 방법을 응용하여 이를 회귀문제에 적용할 수 있게 변형을 한 것이다. 즉, LDAr은 목표값(target)의 차이가 큰 샘플들과 목표값의 차이가 작은 샘플들 간의 거리의 비율을 최대화 하는 것을 목적으로 하게 된다. 제안된 방법을 Yale데이터에 적용하여 임의의 각도로 회전시킨 영상에 대해 회전 각도를 정확히 찾아내는 것을 확인할 수 있었다.

• Korean Journal of Applied Biomechanics
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• v.19 no.4
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• pp.779-791
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• 2009

The purpose of this study is to develop a program that computes the position of the instantaneous center of rotation while an object moves in a circular motion. For this study, a mathematical algorithm was developed and implemented on the experimental data. Data for pitching (40m carry) and putting (4m) strokes were obtained from a skilled female golfer. A computer program (Centering 1.0) calculated the experimental data and found the radius of the instantaneous center of rotation. When the data were taken broadly, the program produced an error distance of radius. When the data were divided gradually, the program produced a very close instantaneous center of rotation. On comparing pitching and putting strokes, putting was found to have a greater radius than pitching. The instantaneous centers of rotation of putting were not in the golfer's body rather, they were 3m away from the club head. The Centering 1.0 program can calculate the instantaneous center of rotation with at least three sets of experimental data.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10b
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• pp.580-582
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• 2003

특징점 기반 지문 인식 방법은 지문 영상의 전처리 과정을 포함한 특징점 추출 과정과 추출된 특징점들의 유사도를 판단하는 정합 과정으로 구성된다. 특징점들의 정합과정을 수행하는 여러 가지 방법들 중 Hausdorff 거리 기반 정합 방법은 이동과 회전이 적은 지문의 특징점들에 대해 빠르게 계산할 수 있는 장점을 갖는다. 그러나, 이 방법은 이동과 회전이 많은 지문 영상의 경우 연산이 많아지는 단점을 가진다. 본 논문에서는 정합을 실행하기 전 지문의 중심점과 지역적인 블럭들의 방향성을 기준으로 정렬을 수행하여 비교되는 지문 특징점간의 회전 오차와 이동 오차를 줄임으로써, 기존의 정합 방법의 불필요한 연산량을 줄일 수 있는 방법을 제안하였다. 제안된 방법을 검증하기 위해 Hausdorff 거리 기반 정합 방법을 구현하고 그것에 대한 결과와 선정렬을 사용한 후의 정합 결과를 실험, 비교하였다. 이때의 평균 Hausdorff 거리는 Genuine의 경우 0.095가 줄어들었고, Improster의 경우 0.655가 늘어나는 성능 향상을 나타냈다.

• Progress in Medical Physics
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• v.15 no.2
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• pp.84-93
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• 2004

Stereotactic radiosurgery (SRS) is a technique that delivers a high dose to a target legion and a low dose to a critical organ through only one or a few irradiations. For this purpose, many mathematical methods for optimization have been proposed. There are some limitations to using these methods: the long calculation time and difficulty in finding a unique solution due to different tumor shapes. In this study, many clinical target shapes were examined to find a typical pattern of tumor shapes from which some possible ideal geometrical shapes, such as spheres, cylinders, cones or a combination, are assumed to approximate real tumor shapes. Using the arrangement of multiple isocenters, optimum variables, such as isocenter positions or collimator size, were determined. A database was formed from these results. The optimization procedure consisted of the following steps: Any shape of tumor was first assumed to an ideal model through a geometry comparison algorithm, then optimum variables for ideal geometry chosen from the predetermined database, followed by a final adjustment of the optimum parameters using the real tumor shape. Although the result of applying the database to other patients was not superior to the result of optimization in each case, it can be acceptable as a plan starling point.

• Progress in Medical Physics
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• v.17 no.4
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• pp.212-223
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• 2006

Positional accuracy of the on-board imager (OBI) isocenter with gantry rotation was presented in this paper. Three different type of automatic evaluation methods of discrepancies between therapeutic and OBI isocenter using digital image processing techniques as well as a procedure stated in the customer acceptance procedure (CAP) were applied to check OBI isocenter migration trends. Two kinds of kV x-ray image set obtained at OBI source angle of $0^{\circ},\;90^{\circ},\;180^{\circ},\;270^{\circ}$ and every $10^{\circ}$ and raw projection data for cone-beam CT reconstruction were used for each evaluation method. Efficiencies of the methods were also estimated. If a user needs to obtain an isocenter variation map with full gantry rotation, a method taking OBI image for every $10^{\circ}$ and fitting with 5th order polynomial was appropriate. However for a mere quality assurance (QA) purpose of OBI isocenter accuracy, it was adequate to use only four OBI Images taken at the OBI source angle of $0^{\circ},\;90^{\circ},\;180^{\circ}\;and\;270^{\circ}$. Maximal discrepancy was 0.44 mm which was observed between the OBI source angle of $90^{\circ}\;and\;180^{\circ}$ OBI isocenter accuracy was maintained below 0.5 mm for a year. Proposed QA program may be helpful to Implement a reasonable routine QA of the OBI isocenter accuracy without great efforts.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.169-172
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• 2001

본 논문은 얼굴의 특징점 추적을 위하여 얼굴 회전 변환과의 크기 변환을 고려한 BMA(Block matching alogorithm)을 이용한 방법을 제안한다. 우선 얼굴의 크기 변화를 구하기 위하여 얼굴 영역을 분리하여 그 면적을 구한다. 이 면적을 이전 프레임에서 구한 얼굴 영역의 면적과 비교하여 크기 비례를 계산한다. 다음으로 각 특징점을 중심으로 하는 8방위 영역의 화소들로 집합을 설정한다. 집합을 설정할 때에는 얼굴의 크기 변화를 고려하여 영역 내 화소들을 포함하는 양을 수정한다. 그리고 새로운 영상에서 화소 집합간의 거리가 가장 작은 화소를 새로운 특징점으로 지정한다. 이 때, 회전 변화를 고려하여 화소 집합의 순서를 순차적으로 바꿔 집합 간 거리를 산출한다. 제안하는 방법은 회전과 크기 변환에 강인한 특성을 보일 뿐 아니라, 단순한 움직임 예측 방법인 BMA보다도 쉽고 빠르게 계산된다.

• Journal of radiological science and technology
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• v.32 no.4
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• pp.453-460
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• 2009

The purpose of this study was to determine the dose distribution and image quality according to slice thickness and BC(beam collimation) in the gantry aperture. CT scans were performed with a 64-slice MDCT(Brilliance 64, Philips, Cleveland, USA) scanner. To determine the dose distribution according to BC, a ionization chamber was placed at isocenter and 5, 10, 15, 20, 25 and 30 cm positions from the isocenter in the 12, 3, 6 and 9 o'clock directions. The dose distribution for phantom scan was also measured using CT head and body dose phantom with five holes at the center of the phantom and the positions of the 12, 3, 6 and 9 o'clock directions. The image noise measurement for different BCs was performed using an AAPM CT phantom. Water-filled block of the phantom was moved by 5 cm or 10 cm to the 12 o'clock direction, and the image noise was measured at the center of the phantom, and the points of 12, 3, 6 and 9 o'clock direction respectively. Some points were placed beyond the scan field of view (SFOV), so that measurement was not possible at that points. The results are as follows: The CTDIw showed a larger decrease as the source goes farther from the iso-center or the BC became wider. The CTDIw depends on the BC width more than the number of the channel of a detector array. The value of CTDIW decreased with increasing BC, but the value decreased 16.6~31.9% in the head phantom scan in air scan and 51.0~64.5% in the body phantom scan. The value of the noise was 3.9~5.9 in the head and 5.3~7.4 in the body except for BC of $2{\times}0.5\;mm$, regardless of the degree of deviation from the iso-center. When a subject was located within the SFOV, the position did not significantly affect image quality even if the subject was out of the center.

• Progress in Medical Physics
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• v.16 no.4
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• pp.166-175
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• 2005

The purpose of this study is to develop the optimization method for adjusting the film isocenter shift and to suggest the quantitative acceptable criteria for film dosimetry after optimization In the dynamic conformal arc radiation therapy (DCAR). The DCAR planning was peformed In 7 patients with brain metastasis. Both absolute dosimetry with ion chamber and relative film dosimetry were peformed throughout the DCAR using BrainLab's micro-multileaf collimator. An optimization method for obtaining the global minimum was used to adjust for the error in the film isocenter shift, which is the largest pan of systemic errors. The mean of point dose difference between measured value using ion chamber and calculated value acquired from planning system was $0.51{\pm}0.43\%$ and maximum was $1.14\%$ with absolute dosimetry These results were within the AAPM criteria of below $5\%$. The translation values of film isocenter shift with optimization were within ${\pm}$1 mm in all patients. The mean of average dose difference before and after optimization was $1.70{\pm}0.35\%$ and $1.34{\pm}0.20\%$, respectively, and the mean ratios over $5\%$ dose difference was $4.54{\pm}3.94\%$ and $0.11{\pm}0.12\%$, respectively. After optimization, the dose differences decreased dramatically and a ratio over $5\%$ dose difference and average dose difference was less than $2\%$. This optimization method is effective in adjusting the error of the film isocenter shift, which Is the largest part of systemic errors, and the results of this research suggested the quantitative acceptable criteria could be accurate and useful in clinical application of dosimetric verification using film dosimetry as follows; film isocenter shift with optimization should be within ${\pm}$1 mm, and a ratio over $5\%$ dose difference and average dose difference were less than $2\%$.