• Journal of radiological science and technology
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• v.16 no.2
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• pp.81-86
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• 1993

Proper evaluation about the penumbra is very important to improve the efficacy of radiation theraphy. There are two kinds of physical penumbra, geometric penumbra and transmission penumbra. In this study, we evaluated the variation of physical penumbra according to the varing energy level, changing the field size and depth. Physical penumbra width was decreased as the source size decreased, and as the SDD increased, but the consideration about the scatter radiation and mechanical stability is an important factor. For the two adjacent beams, upper collimator should be used and especially for Co-60 unit, it is efficient to use the extended collimator.

• Progress in Medical Physics
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• v.20 no.4
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• pp.191-198
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• 2009

In this study, we evaluated an edge detector for small-beam dosimetry. We measured the dose linearity, dose rate dependence, output factor, beam profiles, and percentage depth dose using an edge detector (Model 1118 Edge) for 6-MV photon beams at different field sizes and depths. The obtained values were compared with those obtained using a standard volume ionization chamber (CC13) and photon diode detector (PFD). The dose linearity results for the three detectors showed good agreement within 1%. The edge detector had the best linearity of ${\pm}0.08%$. The edge detector and PFD showed little dose rate dependency throughout the range of 100~600 MU/min, while CC13 showed a significant discrepancy of approximately -5% at 100 MU/min. The output factors of the three detectors showed good agreement within 1% for the tested field sizes. However, the output factor of CC13 compared to the other two detectors had a maximum difference of 21% for small field sizes (${\sim}4{\times}4\;cm^2$). When analyzing the 20~80% penumbra, the penumbra measured using CC13 was approximately two times wider than that using the edge detector for all field sizes. The width measured using PFD was approximately 30% wider for all field sizes. Compared to the edge detector, the 10~90% penumbras measured using the CC13 and PFD were approximately 55% and 19% wider, respectively. The full width at half maximum (FWHM) of the edge detector was close to the real field size, while the other two detectors measured values that were 8~10% greater for all field sizes. Percentage depth doses measured by the three detectors corresponded to each other for small beams. Based on the results, we consider the edge detector as an appropriate small-beam detector, while CC13 and PFD can lead to some errors when used for small beam fields under $4{\times}4\;cm^2$.

• Progress in Medical Physics
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• v.23 no.3
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• pp.138-144
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• 2012

Dose distribution throughout the clinical organ range of motion was analyzed using a respiratory-motion simulator that was equipped with a polymer gel dosimeter and EBT2 film. The normoxic polymer gel dosimeter was synthesized from gelatin, MAA, HQ, THPC and HPLC. The gel dosimeter and EBT2 film were irradiated with Co-60 gamma rays that were moved along the x-axis and y-axis in ${\pm}1.5cm$ steps at five-second intervals. The field size was $5{\times}5cm^2$. The SSD was 80 cm and set to 10 Gy at a depth of 2 cm. The PDD at a depth of 50 mm was 75.2% in the ion chamber, 82.3% in the static state and 86.1% in the dynamic state in the gel dosimeter. The penumbra for the dynamic state target, which was measured using the gel dosimeter, averaged 10.89 mm, this is a 40.5% increase over the penumbra of the static state target of 7.74 mm. In addition, when measuring with gel dosimetry, the value for the penumbra is 36.6% smaller in the static state and 29.4% smaller in the dynamic state compared to measuring with film. The aim of this study was to investigate the dosimetric properties of a normoxic polymethacrylic acid gel dosimeter in static and dynamic states and to evaluate the potentiality as a relative dosimeter for dynamic therapeutic radiation.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.81-87
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• 2006

Purpose: Few researches have been peformed on the dose distribution of the moving organ for radiotherapy so far. In order to simulate the organ motion caused by respiratory function, multipurpose phantom and moving device was used and dosimetric measurements for dose distribution of the moving organs were conducted in this study. The purpose of our study was to evaluate how dose distributions are changed due to respiratory motion. Materials and Methods: A multipurpose phantom and a moving device were developed for the measurement of the dose distribution of the moving organ due to respiratory function. Acryl chosen design of the phantom was considered the most obvious choice for phantom material. For construction of the phantom, we used acryl and cork with density of $1.14g/cm^3,\;0.32g/cm^3$ respectively. Acryl and cork slab in the phantom were used to simulate the normal organ and lung respectively. The moving phantom system was composed of moving device, moving control system, and acryl and cork phantom. Gafchromic film and EDR2 film were used to measure dose ditrbutions. The moving device system may be driven by two directional step motors and able to perform 2 dimensional movements (x, z axis), but only 1 dimensional movement(z axis) was used for this study. Results: Larger penumbra was shown in the cork phantom than in the acryl phantom. The dose profile and isodose curve of Gafchromic EBT film were not uniform since the film has small optical density responding to the dose. As the organ motion was increased, the blurrings in penumbra, flatness, and symmetry were increased. Most of measurements of dose distrbutions, Gafchromic EBT film has poor flatness and symmetry than EDR2 film, but both penumbra distributions were more or less comparable. Conclusion: The Gafchromic EBT film is more useful as it does not need development and more radiation dose could be exposed than EDR2 film without losing film characteristics. But as response of the optical density of Gafchromic EBT film to dose is low, beam profiles have more fluctuation at Gafchromic EBT. If the multipurpose phantom and moving device are used for treatment Q.A, and its corrections are made, treatment quality should be improved for the moving organs.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.2
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• pp.109-113
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• 2008

Purpose: To evaluate the detector dependency in the various collimator size for Stereotactic Radiosugery (SRS). Materials and Methods: This study was performed with 6 MV photon beam (Varian 21EX, Varian, US) and the measurement detectors are used by ion chamber CC01, CC13 (Wellhofer, Germany) and stereotactic diode detector (SFD, Wellhofer, Germany). SRS collimator size was used by ${\varphi}$5, 10, 20, 30 mm (Brain Lab, Germany). Percentage depth dose (PDD) was measured at SSD 100 cm and field size 10×10 cm from individual detectors. Ouput factor was measured by using same setup of PDD and with maximum dose depth. Data was normalized at field size $10{\times}10\;cm$. Beam profile was measured at SSD 100 cm in SRS collimator ${\varphi}$10, 30 mm and field $10{\times}10\;cm$ and a comparison of FWHM (full width half maximum), penumbra width (20~80%). Results: The CC13 detector was overestimated 16% than other detectors from the PDD in the 5 mm collimator. Output factors were underestimated CC01 28%, CC13 72% in the 5 mm collimator and CC01 9.6%, CC13 25% in the 10 mm collimator than the SFD. Maximum difference was 3% at the FWHM of the dose profile in the 10 mm collimator and difference of the 30 mm collimator was 0% at the FWHM. Penumbra width was increased CC01 122%, CC13 194% in the 10 mm collimator and CC01 68%, CC13 185% in the 30 mm collimator than the SFD. Conclusion: It is very important for accurate dosimetry to select a detector in small field. The SFD was considered with the most accurate dosimeter for small collimator dosimetry in this study.

• The Journal of the Acoustical Society of Korea
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• v.18 no.3
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• pp.3-9
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• 1999

This paper presents the study on the rejection capability based on anti-phone modeling for vocabulary independent speech recognition system. The rejection system detects and rejects out-of-vocabulary words which were not included in candidate words which are defined while the speech recognizer is made. The rejection system can be classified into two categories by their implementation methods, keyword spotting method and utterance verification method. The keyword spotting method uses an extra filler model as a candidate word as well as keyword models. The utterance verification method uses the anti-models for each phoneme for the calculation of confidence score after it has constructed the anti-models for all phonemes. We implemented an utterance verification algorithm which can be used for vocabulary independent speech recognizer. We also compared three kinds of means for the calculation of confidence score, and found out that the geometric mean had shown the best result. For the normalization of confidence score, usually Sigmoid function is used. On using it, we compared the effect of the weight constant for Sigmoid function and determined the optimal value. And we compared the effects of the size of cohort set, the results showed that the larger set gave the better results. And finally we found out optimal confidence score threshold value. In case of using the threshold value, the overall recognition rate including rejection errors was about 76%. This results are going to be adapted for stock information system based on speech recognizer which is currently provided as an experimental service by Korea Telecom.

• Progress in Medical Physics
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• v.17 no.4
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• pp.187-191
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• 2006

The purpose of this study was to measure the dose distribution from the moving phantom for the respiratory motion. The phantom for TLD measurement was designed and built for this study based on the multiple plates for placing TLD and film. The TLDs may be inserted at 3 mm intervals in each TLD plate. For the measurements, TLD plate was inserted into the phantom at 1.5 cm ($d_{max}$) depth, and phantom was allowed to move in SI directions in the range of 1 to 2 cm with 0.5 cm interval for 6 MV X-ray beams. Penumbra and FWHM were measured at both moving state and compared stationary. It was found that penumbra increased 0.71 cm at stationary and 2.10 cm at moving state in 2 cm movement, and that FWHM are 7.52 cm for stationary state and 7.02 cm for moving state (2 cm movement). In this study, film was used to compared with TLD results of measurements and simitar results were observed. Therefore, it is expected that TLD moving phantom may be useful for the treatment of tumors that move due to the respiratory motion.

• Journal of the Korean Society of Radiology
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• v.6 no.1
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• pp.19-26
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• 2012

It is very important for early diagnosis and therapy with ischamic cerebral infarction patients. This study was to know the ischemic penumbra lesion which compared CT-perfusion and diffusion weighted MRI(DWMRI) with acute cerebral infarction patients. 12 acute cerebral infarction patients had performed perfusion CT and performed DWMRI. Perfusion images including cerebral blood volume(CBV), cerebral blood flow(CBF), time to peak(TTP) and mean transit time(MTT) maps obtained the values with defect lesion and contralateral normal cerebral hemisphere and DWMRI was measured by signal intensity and compared of lesion size between each perfusion map. All perfusion CT maps showed the perfusion defect lesions in all patients. There were remarkable TTP and MTT delay in perfusion defect lesions. The lesions on CBF map was the most closely correlated with the lesions on DWMRI. The size of perfusion defect lesions on TTP and MTT map was larger than that of lesions on DWMRI, suggesting that MTT map can evaluate the ischemic penumbra. Perfusion CT maps make it possible to evaluate not only ischemic core and ischemic penumbra, but also hemodynamic status in the perfusion defect area. These results demonstrate that perfusion CT can be useful to the diagnosis and treatment in the patients with acute cerebral ischemic infarction.

• The Journal of the Acoustical Society of Korea
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• v.20 no.2
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• pp.27-34
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• 2001

Utterance verification is used in variable vocabulary word recognition to reject the word that does not belong to in-vocabulary word or does not belong to correctly recognized word. Utterance verification is an important technology to design a user-friendly speech recognition system. We propose a new utterance verification algorithm for no-training utterance verification system based on the minimum verification error. First, using PBW (Phonetically Balanced Words) DB (445 words), we create no-training anti-phoneme models which include many PLUs(Phoneme Like Units), so anti-phoneme models have the minimum verification error. Then, for OOV (Out-Of-Vocabulary) rejection, the phoneme-based confidence measure which uses the likelihood between phoneme model (null hypothesis) and anti-phoneme model (alternative hypothesis) is normalized by null hypothesis, so the phoneme-based confidence measure tends to be more robust to OOV rejection. And, the word-based confidence measure which uses the phoneme-based confidence measure has been shown to provide improved detection of near-misses in speech recognition as well as better discrimination between in-vocabularys and OOVs. Using our proposed anti-model and confidence measure, we achieve significant performance improvement; CA (Correctly Accept for In-Vocabulary) is about 89％, and CR (Correctly Reject for OOV) is about 90％, improving about 15-21％ in ERR (Error Reduction Rate).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.2
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• pp.70-80
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• 2000

Princeton Ocean Model (POM) is modified to construct a three-dimensional, semi-implicit hydro¬dynamic model with a wetting-and-drying scheme. The model employs semi-implicit treatment of the barotropic pressure gradient terms and the vertical mixing terms in the momentum equations, and the velocity divergence term in the vertically-integrated continuity equation. Such treatment removes the external mode and thus the mode splitting scheme in POM, allowing the semi-implicit model to use a larger time step. Applied to hypothetical systems, both the semi-implicit model and POM give nearly the same results. The semi-implicit model, however, runs approximately 4.4 times faster than POM showing its improved computational efficiency. Applied to a hypothetical system with intertidal flats, POM employing the mode splitting scheme produces noises at the intertidal flats, that propagate into the main channel resulting in unstable current velocities. Despite its larger time step, the semi-implicit model gives stable current velocities both at the intertidal flats and main channel. The semi-implicit model when applied to Kyeonggi Bay gives a good reproduction of the observed tides and tidal currents throughout the modeling domain, demonstrating its prototype applicability.