• Journal of the Korean Professional Engineers Association
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• v.19 no.1
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• pp.3-11
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• 1986

The analysis of Geotechnical stability problems by the limit equilibrium method involve assuming the shape of the failure and then investigating many surfaces of the shape to identify the one on which failure seems most likely to occur. These arbitrary assumptions most frequently concern to the locations or directions of side force on slice and the overall factor of safety is considered identical to the local factor of safety. In this paper, let the factor of safety of a slope at wedge block stage differently, when an upper part of the potential sliding mass has a simple active stress field and the lower part of the passive stress field and overall factor of safety is obtained by the average of local factor and computer program based on the modified wedge Method is proposed for this thesis. The new algorithm based on tile modified new method is made for estimating the safety factor of Earth Dam. Compared with conventional method for many cases tile average values of the factor of safety determined by the modified new method are very nearly the same. For all of the cases studied the difference was found 0.03. Finally this new method is thought to be very useful in slope stability analysis.

• Progress in Medical Physics
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• v.8 no.2
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• pp.3-17
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• 1997

Because a wedged beam consists of attenuated primary photons and scattered radiations from wedge, the spectrum of the wedged beam does not coincide with that of an open beam with same geometry. The aims of current report are to get exact information about whether effects of 15-60$^{\circ}$ wedge for 4 -10 MV photon beams should be considered for dose calculation or not, and to suggest a reference condition for measurement of wedge transmission factor. Percent depth dose of both open and wedged fields with angles of 15, 30, 45, 60$^{\circ}$ for beams of 4 MV(Clinac 4/100, Varian), two 6 MV(Clinac 6/100 and Clinac 2100C, Varian), 10 MV(Clinac 2100C, Varian) X-rays were measured to 30cm deep in water using ionization chambers. Hardening factors of photon beams were calculated with measured PDDs. Both field size factors and transmission factors of wedge filters were measured at d$_{max}$ in water. Beam hardening factors of wedged fields of 4 and 6 MV X-ray were larger than 1 for all wedge angles, field sizes and depths deeper than d$_{max}$ Beam hardening factors for wedge angles 15, 30, 45, 60$^{\circ}$ for 10$\times$10cm were respectively 1.010, 1.014, 1.023 and 1.034 for 4MV X-ray, 1.005, 1.008, 1.019, and 1.024 for 6MV X-ray of Clinac 6/100, 1.011, 1.021, 1.032, 1.036 for 6MV X-ray of Clinac 2100C, and 1.008, 1.012, 1.012 and 1.012 for 10MV X-ray. Beam hardening factors of 10MV X-ray were 1 within 1.2％ difference for all wedge angles, depths and field sizes. It was made clear that for 6MV X-rays, the beam hardening factor depends on treatment machine. The relationship of the factor and depth was linear. Field size factor at d$_{max}$ was independent of wedge angle except for the field of 15$\times$15cm. and maximum difference of the field size factors for the field size was 1.4％ for 4MV X-ray. When the wedge factor is determined, dependence of the factor on field size is negligible at d$_{max}$ but should be considered at deeper depth. Calculating dose distribution or MU, the beam hardening factor should be applied for 4~6MV X-ray beams, but might not be considered for 10MV beam. When wedge transmission factor was determined at d$_{max}$ or in air, field size factors for open field are also applicable to wedged fields, but otherwise, field size factor for each wedge or wedge factor depending on field size should be applied.

• 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.

• Journal of radiological science and technology
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• v.24 no.2
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• pp.49-52
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• 2001

We compared the characteristics of Siemens virtual wedge device with physical wedges for clinical application. We investigated the characteristics of virtual and physical wedges for various wedge angles (15, 30, 45, and 60) using 6- and 15-MV photon beams. Wedge factors were measured in water using an ion chamber for various field sizes and depths. In case of virtual wedge device, as upper jaw moves during irradiation, wedge angles were estimated by accumulated doses. These measurements were performed at off-axis points perpendicular to the beam central axis in water for a $15\;cm\;{\times}\;20\;cm$ radiation field size at the depth of 10 cm. Surface doses without and with virtual or physical wedges were measured using a parallel plate ion chamber at surface. Field size was $15\;cm\;{\times}\;20\;cm$ and a polystyrene phantom was used. For various field sizes, virtual and physical wedge factors were changed by maximum 2.1% and 3.9%, respectively. For various depths, virtual and physical wedge factors were changed by maximum 1.9% and 2.9%, respectively. No major difference was found between the virtual and physical wedge angles and the difference was within 0.5. Surface dose with physical wedge was reduced by maximum 20% (x-ray beam : 6 MV, wedge angle : 45, SSD : 80 cm) relative to one with virtual wedge or without wedge. Comparison of the characteristics of Siemens virtual wedge device with physical wedges was performed. Depth dependence of virtual wedge factor was smaller than that of physical wedge factor. Virtual and physical wedge factors were nearly independent of field sizes. The accuracy of virtual and physical wedge angles was excellent. Surface dose was found to be reduced using a physical wedge.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.1
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• pp.53-62
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• 1989

In order to determine the form and the length of saline wedge, it is necessary to evaluate interfacial friction factor. Hetherto one dimensional two-layer flow model which assumed pressure as the hydrostatic pressure distribution has been well used to the calculation of saline wedge form, it just then stands in need of relevant interfacial friction factor. For example, in the case where we calculate back to interfacial friction factor out of saline wedge form obtained at a laboratory open channel with comparatively narrow width, it is needed to correct the side-wall effect of a channel, if generally negligible in the river. In this study, we confirmed the influence of a side-wall upon the lateral velocity distributions at laboratory channel and then examined in detail the value of interfacial friction factor in the case where it was corrected by the side-wall effect and not corrected. And then we make clear the influence of a side-wall upon the arrested saline wedge and interfacial faction factor from these results.

• Radiation Oncology Journal
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• v.17 no.1
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• pp.78-83
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• 1999

Purpose : We have compared the characteristics of Siemens virtual wedge device with physical wedges for clinical application. Materials and Methods : We investigated the characteristics of virtual and physical wedges for various wedge angles (15, 30, 45, and 60$^{\circ}$) using 6- and 15MV photon beams. Wedge factors were measured in water using an ion chamber for various field sizes and depths. In case of virtual wedge device, as upper jaw moves during irradiation, wedge angles were estimated by accumulated doses. These measurements were performed at off-axis points perpendicular to the beam central axis in water for a 15cm${\times}$20cm radiation field size at the depth of loom. Surface doses without and with virtual or physical wedges were measured using a parallel plate ion chamber at surface. Field size was 15cm H20cm and a polystyrene phantom was used. Results : For various field sizes, virtual and physical wedge factors were changed by maximum 2.1% and 3.9%) , respectively. For various depths, virtual and physical wedge factors were changed by maximum 1.9% and 2.9%, respectively. No major difference was found between the virtual and physical wedge angles and the difference was within 0.5$^{\circ}$ . Suface dose with physical wedge was reduced by maximum 20% (x-ray beam :6 MV, wedge angle:45$^{\circ}$, 550: 80 cm) relative to one with virtual wedge or without wedge. Conclusions : Comparison of the characteristics of Siemens virtual wedge device with physical wedges was performed. Depth dependence of virtual wedge factor was smaller than that of physical wedge factor. Virtual and physical wedge factors were nearly independent of field sizes. The accuracy of virtual and physical wedge angles was excellent. Surface dose was found to be reduced using physical wedge.

• Progress in Medical Physics
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• v.12 no.2
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• pp.125-131
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• 2001

We was investigate the dosimetric characteristics of the virtual wedge and it compared to the conventional fixed wedge. Also we was evaluate the quality factor of the experimental multi-channel dosimetry system for virtual wedge. Recently virtual wedge technique and wedge fraction methods are available through the computer controlled asymmetric collimator or the independent jaw in medical linear accelerator for radiation therapy. The dosimetric characteristics are interpreted by radiation field analyzer RFA-7 system and PTW-UNIDOS system. Experimental multi-channel dosimetry system for virtual wedge was consists of the electrometer, the solid detector and array phantom. The solid detectors were constructed using commercially diodes for the assessment of quality assurance in radiotherapy. And it was used for the point dose measuring and field size scanning. The semiconductor detector and ion chamber were positioned at a dmax, 5 cm, 10 cm, 20 cm depth and its specific ratio was determined using a scanning data. Wedge angles in fixed and virtual type are compared with measurements in water phantom and it is shown that the wedge angle 15$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$were agree within 1$^{\circ}$ degree in 6, 10 MV photon beams. In PDD and beam flatness, experimental multi-channel disimetry system was capable of reproduceing the measured values usually to within $\pm$2.1% the statistical uncertainties of the data. It was used to describe dosimetric characteristics of virtual wedge in clinical photon beams. Also we was evaluate optimal use of the virtual wedge and improve the quality factor of the experimental multi-channel dosimetry system for virtual wedge.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.1
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• pp.53-60
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• 2010

Purpose: We try to calculate EDW-factor easily with the formula applies essential data of EDW-factor and evaluate the validity through a measurement. Materials and Methods: We used the given value of GSTT (Golden Segmented Treatment Table) for the calculation of the EDW-factor. As to the experimental device, 0.6 cc farmer-type ion-chamber, an electrometer and water- phantom were used. A measurement was made at the maximum dose depth of the photon beam energy 6 MV and 15 MV under the condition that SSD (Source to Surface Distance) was 100 cm. The angle of the EDW (Enhanced Dynamic Wedge) which we use in an experiment was 60 degree, 30 degree, 20 degree in the Y1-OUT direction. We used Eclipse planning system (Varian, USA) as RTP system and the EDW-factor was calculated about all fields and EDW direction. In order to show the EDW-factor feature, a measurement was made at the selected field that verify the influence of the dependability about X, Y jaw and off-axis field. Results: When we change the Y1 field, it influence on the EDW-Factor and measured value. But the error between measured values and calculated values was less than 1%. The experimental result indicated the tendency that the error of the result of calculation and measured value becomes smaller as the EDW angle become smaller whether the calculation point (measurement point) and iso-center are same or not. The influence of the field size and energy did not show up. We simulated with the same condition using the RTP system. And we found that it makes no difference between the MU which is calculated manually by applying the EDW-Factor obtained from the commercial program and the value which is calculated by using RTP system. Conclusion: We excluded fitting value from well-known EDW-Factor formula and calculated EDW-factor with the formula applies essential data of EDW-factor only. As a result, there are no significant difference between the measured value and calculated value and it showed errors less than 1%. Also, we implemented the commercial program to calculate EDW-Factor conveniently without measure a factor on each field.

• Progress in Medical Physics
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• v.18 no.1
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• pp.7-12
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• 2007

In the radiation therapy for breast cancer patients, wedge shaped compensators are essentially used to achieve appropriate dose distribution because of thickness difference according to breast shapes. Tangential Irradiation technique has usually been applied to radiation therapy for breast cancer patients treated with breast conservative surgery. When a primary beam is incident on wedge shaped compensators from medial direction In tangential irradiation technique, low energy scattered radiation is generated and gives additional dose to the breast surface. As a method to reduced additional dose to breast surface, the use of virtual wedge shaped compensator is possible. Eclipse radiation treatment planning (RTP) systems Installed at our institution have virtual wedge shaped compensator for radiation therapy treatment planning. The dose distributions of 15, 30, 45, 60 degree physical wedges and virtual wedges were measured and compared. Results showed that there was no significant differences In symmetry of $10{\times}10$ field among various wedge angles. When the transmission factor was compared, transmission factor Increased linearly as the wedge angle Increased. These results Indicates that the appilcation of virtual wedge in clinical use is appropriate.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.2
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• pp.72-80
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• 1991

This study presents the behavior of unsteady saline wedge in which it is examined velocity profile variations at the lower layer (inner wedge) and wedge tip responses to a tidal action in a rectangular open channel. Unsteady saline wedge has just tidal excursions corresponding to tidal amplitudes at the river mouth, although two wedge tips in flood and ebb tide remarkably have different shapes. Maximum velocities at the lower layer appear immediately from high water to low water level (or low to high water). Numerical computation results obtained by only just interfacial friction factor at the steady state show satisfactory agreements with experimental data. However, the numerical model on one-demensional two-layer flor still has some problems to date.