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고해상도 위성영상을 이용한 북한지역 지리정보 구축 실험연구
사공호상,한선희,박진형,서기환 한국지리정보학회 2004 한국지리정보학회지 Vol.7 No.4
남북한간 경제협력과 교류가 어느 때 보다도 활발하게 추진됨에 따라 북한지역에 대한 지리정보의 수요가 날로 증가하고 있다. 그러나 아직까지 이렇다 할 방법을 찾지 못하고 있는 실정이다. 이에 따라. 이 연구에서는 고해상도 위성영상을 이용하여 북한지역의 지리정보를 획득하는 방안을 모색하였다. 실효성 있는 연구결과를 도출하기 위하여 북한의 사례지역에 대해 실제로 지리정보를 구축하고, 위치정확도도 검중하였다. 실험연구 결과, 총 52개 망목의 지리정보를 추출하였다. 또한 스테레오 영상의 수평 및 수직오차는 각각 4.6m와 09m로 상당히 정확하였으며, 단영상의 수평오차는 약 9m 정도를 스테레오 영상보다는 크지만 북만관련 업무나 연구의 기초자료로 만족할 수 있는 수준으로 나타났다. As economic cooperation and exchanges between North and South Korea have been glowing much more than before, the demand for geographic information on North Korea is recently increasing. In fact, there is no specific method to be provided with geographic information on North Korea. In this regard, the study searched a method to collect geographic information on North Korea by using the high spatial resolution satellite image. In order to produce its best result, the study collected the geographic information on the case study area and ensured the location accuracy. This study produced total 52 items of geographic information on North Korea. Horizontal and vertical errors of stereo image, which are 4.6m and 0. 9m respectively, showed high accuracy. In addition, even though the horizontal error of single image is 9m, which is bigger than that of stereo image, there is no doubt that it can be used as basic data for North Korean studies and related projects.
Jin, Hosang,Jesseph, Fredrick B.,Ahmad, Salahuddin Korean Society of Medical Physics 2014 의학물리 Vol.25 No.2
A Varian Portal Dosimetry system was compared to an isocentrically mounted MapCHECK 2 diode array for volumetric modulated arc therapy (VMAT) QA. A Varian TrueBeam STx with an aS-1000 digital imaging panel was used to acquire VMAT QA images for 13 plans using four photon energies (6, 8, 10 and 15 MV). The EPID-based QA images were compared to the Portal Dose Image Prediction calculated in the Varian Eclipse treatment planning system (TPS). An isocentrically mounted Sun Nuclear MapCHECK 2 diode array with 5 cm water-equivalent buildup was also used for the VMAT QAs and the measurements were compared to a composite dose plane from the Eclipse TPS. A ${\gamma}$ test was implemented in the Sun Nuclear Patient software with 10% threshold and absolute comparison at 1%/1 mm (dose difference/distance-to-agreement), 2%/2 mm, and 3%/3 mm criteria for both QA methods. The two-tailed paired Student's t-test was employed to analyze the statistical significance at 95% confidence level. The average ${\gamma}$ passing rates were greater than 95% at 3%/3 mm using both methods for all four energies. The differences in the average passing rates between the two methods were within 1.7% and 1.6% of each other when analyzed at 2%/2 mm and 3%/3 mm, respectively. The EPID passing rates were somewhat better than the MapCHECK 2 when analyzed at 1%/1 mm; the difference was lower for 8 MV and 10 MV. However, the differences were not statistically significant for all criteria and energies (p-values >0.05). The EPID-based QA showed large off-axis over-response and dependence of ${\gamma}$ passing rate on energy, while the MapCHECK 2 was susceptible to the MLC tongue-and-groove effect. The two fluence-based QA techniques can be an alternative tool of VMAT QA to each other, if the limitations of each QA method (mechanical sag, detector response, and detector alignment) are carefully considered.
Jin, Hosang,Palta, Jatinder,Suh, Tae-Suk,Kim, Siyong Wiley (John WileySons) 2008 Medical physics Vol.35 No.3
<P>Multileaf collimator-based intensity modulated radiation therapy (IMRT) is complex because each intensity modulated field consists of hundreds of subfields, each of which is associated with an intricate interplay of uncertainties. In this study, the authors have revised the previously introduced uncertainty model to provide an a priori accurate prediction of dose uncertainty during treatment planning in IMRT. In the previous model, the dose uncertainties were categorized into space-oriented dose uncertainty (SOU) and nonspace-oriented dose uncertainty (NOU). The revised model further divided the uncertainty sources into planning and delivery. SOU and NOU associated with a planning system were defined as inherent dose uncertainty. A convolution method with seven degrees of freedom was also newly applied to generalize the model for practical clinical cases. The model parameters were quantified through a set of measurements, accumulated routine quality assurance (QA) data, and peer-reviewed publications. The predicted uncertainty maps were compared with dose difference distributions between computations and 108 simple open-field measurements using a two-dimensional diode array detector to verify the validity of the model parameters and robustness of the generalized model. To examine the applicability of the model to overall dose uncertainty prediction in IMRT, a retrospective analysis of QA measurements using the diode array detector for 32 clinical IM fields was also performed. A scatter diagram and a correlation coefficient were employed to investigate a correlation of the predicted dose uncertainty distribution with the dose discrepancy distribution between calculation and delivery. In addition, a gamma test was performed to correlate failed regions in dose verification with the dose uncertainty map. The quantified model parameters well correlated the predicted dose uncertainty with the probable dose difference between calculations and measurements. It was visually validated with the scatter diagrams. The average correlation coefficient between uncertainty and dose difference of 108 verification measurements was 0.80 +/- 0.04, indicating a strong linear correlation. In the clinical IM field studies, the dose uncertainty map mimicked the probable dose difference distribution. The average correlation coefficient between the overall dose uncertainty and the dose difference of 32 QA measurements (total 13 184 comparison points) was 0.75 +/- 0.07, which also indicated a strong linear correlation between them. The failed regions of the gamma test remarkably corresponded to relatively high dose uncertainty. In conclusion, the dose uncertainty map was able to highlight high dose uncertainty regions, where more care should be taken during the treatment plan. The a priori accurate prediction of dose uncertainty in IMRT will significantly improve the treatment plan evaluation process, thus improving the quality of radiation treatments.</P>
Jin, Hosang,Chung, Heetaek,Liu, Chihray,Palta, Jatinder,Suh, Tae-Suk,Kim, Siyong Wiley (John WileySons) 2005 Medical physics Vol.32 No.6
<P>Based on statistical approach, a novel dose uncertainty model was introduced considering both nonspatial and spatial dose deviations. Non-space-oriented uncertainty is mainly caused by dosimetric uncertainties, and space-oriented dose uncertainty is the uncertainty caused by all spatial displacements. Assuming these two parts are independent, dose difference between measurement and calculation is a linear combination of nonspatial and spatial dose uncertainties. Two assumptions were made: (1) the relative standard deviation of nonspatial dose uncertainty is inversely proportional to the dose standard deviation sigma, and (2) the spatial dose uncertainty is proportional to the gradient of dose. The total dose uncertainty is a quadratic sum of the nonspatial and spatial uncertainties. The uncertainty model provides the tolerance dose bound for comparison between calculation and measurement. In the statistical uncertainty model based on a Gaussian distribution, a confidence level of 3sigma theoretically confines 99.74% of measurements within the bound. By setting the confidence limit, the tolerance bound for dose comparison can be made analogous to that of existing dose comparison methods (e.g., a composite distribution analysis, a gamma test, a chi evaluation, and a normalized agreement test method). However, the model considers the inherent dose uncertainty characteristics of the test points by taking into account the space-specific history of dose accumulation, while the previous methods apply a single tolerance criterion to the points, although dose uncertainty at each point is significantly different from others. Three types of one-dimensional test dose distributions (a single large field, a composite flat field made by two identical beams, and three-beam intensity-modulated fields) were made to verify the robustness of the model. For each test distribution, the dose bound predicted by the uncertainty model was compared with simulated measurements. The simulated measurements were within the tolerance bound as expected by a statistical prediction of the model. Using the dose uncertainty distributions, an uncertainty length (uncertainty area and uncertainty volume for two-dimensional and three-dimensional, respectively) histogram (a plot of the dose uncertainty of 1sigma received by a length of field) was made. The histogram provides additional information on superiority of a treatment plan in terms of uncertainty. In summary, the uncertainty model provides the dose comparison tool as well as the evaluation tool of a treatment planning system.</P>
Hosang Jin,Fredrick B. Jesseph,Salahuddin Ahmad 한국의학물리학회 2014 의학물리 Vol.25 No.2
A Varian Portal Dosimetry system was compared to an isocentrically mounted MapCHECK 2 diode array forvolumetric modulated arc therapy (VMAT) QA. A Varian TrueBeam STx with an aS-1000 digital imaging panelwas used to acquire VMAT QA images for 13 plans using four photon energies (6, 8, 10 and 15 MV). TheEPID-based QA images were compared to the Portal Dose Image Prediction calculated in the Varian Eclipsetreatment planning system (TPS). An isocentrically mounted Sun Nuclear MapCHECK 2 diode array with 5 cmwater-equivalent buildup was also used for the VMAT QAs and the measurements were compared to a compositedose plane from the Eclipse TPS. A γtest was implemented in the Sun Nuclear Patient software with 10%threshold and absolute comparison at 1%/1 mm (dose difference/distance-to-agreement), 2%/2 mm, and 3%/3mm criteria for both QA methods. The two-tailed paired Student’s t-test was employed to analyze the statisticalsignificance at 95% confidence level. The average γpassing rates were greater than 95% at 3%/3 mm usingboth methods for all four energies. The differences in the average passing rates between the two methods werewithin 1.7% and 1.6% of each other when analyzed at 2%/2 mm and 3%/3 mm, respectively. The EPID passingrates were somewhat better than the MapCHECK 2 when analyzed at 1%/1 mm; the difference was lower for8 MV and 10 MV. However, the differences were not statistically significant for all criteria and energies (p-values>0.05). The EPID-based QA showed large off-axis over-response and dependence of γpassing rate on energy,while the MapCHECK 2 was susceptible to the MLC tongue-and-groove effect. The two fluence-based QAtechniques can be an alternative tool of VMAT QA to each other, if the limitations of each QA method (mechanicalsag, detector response, and detector alignment) are carefully considered.