• Current Optics and Photonics
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• v.2 no.5
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• pp.474-481
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• 2018

We propose a polarization phase-shifting technique to investigate the thickness of $Ta_2O_5$ thin films deposited on BK7 substrates, using a modified Sagnac interferometer. Incident light is split by a polarizing beam splitter into two orthogonal linearly polarized beams traveling in opposite directions, and a quarter-wave plate is inserted into the common path to create an unbalanced phase condition. The linearly polarized light beams are transformed into two circularly polarized beams by transmission through a quarter-wave plate placed at the output of the interferometer. The proposed setup, therefore, yields rotating polarized light that can be used to extract a relative phase via the self-reference system. A thin-film sample inserted into the cyclic path modifies the output signal, in terms of the phase retardation. This technique utilizes three phase-shifted intensities to evaluate the phase retardation via simple signal processing, without manual adjustment of the output polarizer, which subsequently allows the thin film's thickness to be determined. Experimental results show that the thicknesses obtained from the proposed setup are in good agreement with those acquired by a field-emission scanning electron microscope and a spectroscopic ellipsometer. Thus, the proposed interferometric arrangement can be utilized reliably for non-contact thickness measurements of transparent thin films and characterization of optical devices.

• Progress in Medical Physics
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• v.5 no.1
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• pp.87-99
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• 1994

Purpose : The determination of electron beam output factor was investigated from individual applicator for various energy of ML-15MDX linear accelerator. The output factor of electron beam was extended from square to rectangular field in individual applicator size through with a least-square fit to a polynomial expression. Materials : In this experiments. the measurement of output was obtained from 2${\times}$cm$^2$ to 20${\times}$20cm$^2$ of field size in different applicator size for 4 to 15 MaV electron beam energy. The output factor was defined as the ratio of maximum dose output on the central axis of the field of individual applicator size to that of a given field size. Applicator factors were derived from comparing with the output dose of reference field size 10${\times}$10cm$^2$. The thickness of block was specially designed as 10mm in thickness of Lipowitz metal for field shaping in all electron energy. Two types of output curves are included as output factors versus side of square fields and that of variable side length for X and Y in one-dimensional to compare the expected values to that of experiments. Results : Expected output factors of rectangular which was derived from that of square fields in individual applicator size from 2${\times}$2cm$^2$ to 20${\times}$20cm$^2$ in different electron energy was very closed to that of experimental measurements within 2% uncertainty. However 1D method showed a 3% discrepancy in small rectangular field for low energy electron beam. Conclusion : Emperical non-linear polynomial regressions of square root and 1D method were performed to determin the output factor in various field size and electron energy. The expected output of electron beam of square root method for square field and 1D method for rectangular field were very closed to that of measurement in all selected electron beam energy.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.1
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• pp.25-29
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• 2008

Purpose: To monitor the changes of location of prostate gland using DIPS and to examine the adjustment and proton beam therapy depending on the movement of prostate gland in proton beam therapy for prostate gland in which a fiducial gold marker was inserted. Materials and Methods: This study was conducted in ten patients with prostate cancer who received proton beam therapy since April of 2008. To monitor the change of prostate location, three fiducial gold markers were inserted prior to the treatment. To minimize the movement of prostate gland, patients were recommended to urinate prior to the treatment, to intake a certain amount of water and to concomitantly undergo rectal balloon. In these patients, the set-up position was identical to that for a CT-simulation. The PA (posterior-anterior) and lateral images were obtained using both DIPS (digital image positioning system) and a plain radiography, and they were compared between the two imaging modalities. Thus, the changes of the location of fiducial gold marker were assessed based on three coordinates (x, y, z) and then adjusted. This was followed by proton beam therapy. Results: Images which were taken using a plain radiography were compared with those which were taken using DIPS. In ten patients, according to a reference bony marker, the mean changes of the location of fiducial gold marker based on an iso-center were X-axis: $\pm$0.116 cm, Y-axis: $\pm$0.19 cm and Z-axis: $\pm$0.176 cm. These ten patients showed a difference in the changes of location of prostate gland and it ranged between RT: 0.04 cm and RT: 0.24 cm on the X-axis; between Inf: 0.03 cm and Sup: 0.42 cm on the Y-axis; and Post: 0.05 cm and Ant: 0.35 cm on the Z-axis. Conclusion: To minimize the movement of prostate gland, as the pre-treatment prior to the treatment. In all the patients, however, three fiducial gold markers showed a daily variation which were inserted in the prostate gland. Based on the above data, Thus, the requirement of gold marker matching system depending on the daily variation in the proton beam therapy for which more accurate establishment of target was confirmed. It is assumed that an accurate effect of proton beam therapy would be enhanced by adjusting the target-center depending on the location change of prostate gland using DIPS which was used in the current study.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.11
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• pp.4717-4721
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• 2014

Background: Dosimetric comparison of two dimensional (2D) radiography and three-dimensional computed tomography (3D-CT) based dose distributions with high-dose-rate (HDR) intracavitry radiotherapy (ICRT) for carcinoma cervix, in terms of target coverage and doses to bladder and rectum. Materials and Methods: Sixty four sessions of HDR ICRT were performed in 22 patients. External beam radiotherapy to pelvis at a dose of 50 Gray in 27 fractions followed by HDR ICRT, 21 Grays to point A in 3 sessions, one week apart was planned. All patients underwent 2D-orthogonal and 3D-CT simulation for each session. Treatment plans were generated using 2D-orthogonal images and dose prescription was made at point A. 3D plans were generated using 3D-CT images after delineating target volume and organs at risk. Comparative evaluation of 2D and 3D treatment planning was made for each session in terms of target coverage (dose received by 90%, 95% and 100% of the target volume: D90, D95 and D100 respectively) and doses to bladder and rectum: ICRU-38 bladder and rectum point dose in 2D planning and dose to 0.1cc, 1cc, 2cc, 5cc, and 10cc of bladder and rectum in 3D planning. Results: Mean doses received by 100% and 90% of the target volume were $4.24{\pm}0.63$ and $4.9{\pm}0.56$ Gy respectively. Doses received by 0.1cc, 1cc and 2cc volume of bladder were $2.88{\pm}0.72$, $2.5{\pm}0.65$ and $2.2{\pm}0.57$ times more than the ICRU bladder reference point. Similarly, doses received by 0.1cc, 1cc and 2cc of rectum were $1.80{\pm}0.5$, $1.48{\pm}0.41$ and $1.35{\pm}0.37$ times higher than ICRU rectal reference point. Conclusions: Dosimetric comparative evaluation of 2D and 3D CT based treatment planning for the same brachytherapy session demonstrates underestimation of OAR doses and overestimation of target coverage in 2D treatment planning.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.1
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• pp.11-19
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• 2014

Purpose : To derive the most appropriate factors by considering the effects of the major factors when applied to the optimization algorithm, thereby aiding the effective designing of a ideal treatment plan. Materials and Methods : The eclipse treatment planning system(Eclipse 10.0, Varian, USA) was used in this study. The PBC (Pencil Beam Convolution) algorithm was used for dose calculation, and the DVO (Dose Volume Optimizer 10.0.28) Optimization algorithm was used for intensity modulated radiation therapy. The experimental group consists of patients receiving intensity modulated radiation therapy for the head and neck cancer and dose prescription to two planned target volume was 2.2 Gy and 2.0 Gy simultaneously. Treatment plan was done with inverse dose calculation methods utilizing 6 MV beam and 7 fields. The optimal algorithm parameter of the established plan was selected based on volume dose-priority(Constrain), dose fluence smooth value and the impact of the treatment plan was analyzed according to the variation of each factors. Volume dose-priority determines the reference conditions and the optimization process was carried out under the condition using same ratio, but different absolute values. We evaluated the surrounding normal organs of treatment volume according to the changing conditions of the absolute values of the volume dose-priority. Dose fluence smooth value was applied by simply changing the reference conditions (absolute value) and by changing the related volume dose-priority. The treatment plan was evaluated using Conformal Index, Paddick's Conformal Index, Homogeneity Index and the average dose of each organs. Results : When the volume dose-priority values were directly proportioned by changing the absolute values, the CI values were found to be different. However PCI was $1.299{\pm}0.006$ and HI was $1.095{\pm}0.004$ while D5%/D95% was $1.090{\pm}1.011$. The impact on the prescribed dose were similar. The average dose of parotid gland decreased to 67.4, 50.3, 51.2, 47.1 Gy when the absolute values of the volume dose-priority increased by 40,60,70,90. When the dose smooth strength from each treatment plan was increased, PCI value increased to $1.338{\pm}0.006$. Conclusion : The optimization algorithm was more influenced by the ratio of each condition than the absolute value of volume dose-priority. If the same ratio was maintained, similar treatment plan was established even if the absolute values were different. Volume dose-priority of the treatment volume should be more than 50% of the normal organ volume dose-priority in order to achieve a successful treatment plan. Dose fluence smooth value should increase or decrease proportional to the volume dose-priority. Volume dose-priority is not enough to satisfy the conditions when the absolute value are applied solely.

• The korean journal of orthodontics
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• v.39 no.5
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• pp.300-309
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• 2009

Objective: The purpose of this study was to evaluate the correlation between menton deviation and dental compensation in facial asymmetry. Methods: Tooth axis and distance of first molar and canine to the reference plane were investigated by cone-beam computerized tomography. The subjects consisted of 50 patients with asymmetric mandibles (male 21, female 29, mean age 24.3 years). Control groups were also assessed (male 11, female 9, mean age 25.6 years). Nine measurements (5 linear measurements and 4 angular measurements) were measured in order to evaluate the correlation between menton deviation and the linear and angular difference of first molar and canine in the deviated and none-deviated sides using the defined MPR images. The differences between deviated and non-deviated side, according to menton deviation, were statistically analyzed using stepwise multiple regression analysis. Results: From the result, Menton deviation was negatively correlated with mandibular first molar's angular measurement (${\Delta\angle}LM6$-Mn plane (dev.-ndev.)) and positively with maxillary fist molar's angular measurement (${\Delta\angle}UM6$-FH plane (dev.-ndev.)) (p < 0.01). Two angular measurements (${\Delta\angle}LM6$-Mn plane (dev.-ndev.), ${\Delta\angle}UM6$-FH plane (dev.-ndev.)) explained the variability in menton deviation with a significant $r^2$ value of 0.589. Conclusions: This study suggests that the tooth axis of upper and lower first molars leans towards the deviated side of Menton when there is mandibular asymmetry with Menton deviation.

• Progress in Medical Physics
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• v.28 no.3
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• pp.111-121
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• 2017

Verification of dose distribution is an essential part of ensuring the treatment planning system's (TPS) calculated dose will achieve the desired outcome in radiation therapy. Each measurement have uncertainty associated with it. It is desirable to reduce the measurement uncertainty. A best approach is to reduce the uncertainty associated with each step of the process to keep the total uncertainty under acceptable limits. Point dose patient specific quality assurance (QA) is recommended by American Association of Medical Physicists (AAPM) and European Society for Radiotherapy and Oncology (ESTRO) for all the complex radiation therapy treatment techniques. Relative and absolute point dose measurement methods are used to verify the TPS computed dose. Relative and absolute point dose measurement techniques have a number of steps to measure the point dose which includes chamber cross calibration, electrometer reading, chamber calibration coefficient, beam quality correction factor, reference conditions, influences quantities, machine stability, nominal calibration factor (for relative method) and absolute dose calibration of machine. Keeping these parameters in mind, the estimated relative percentage uncertainty associated with the absolute point dose measurement is 2.1% (k=1). On the other hand, the relative percentage uncertainty associated with the relative point dose verification method is estimated to 1.0% (k=1). To compare both point dose measurement methods, 13 head and neck (H&N) IMRT patients were selected. A point dose for each patient was measured with both methods. The average percentage difference between TPS computed dose and measured absolute relative point dose was 1.4% and 1% respectively. The results of this comparative study show that while choosing the relative or absolute point dose measurement technique, both techniques can produce similar results for H&N IMRT treatment plans. There is no statistically significant difference between both point dose verification methods based upon the t-test for comparing two means.

• Journal of the Korean Vacuum Society
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• v.7 no.3
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• pp.176-186
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• 1998

Pure Pt, Co and their alloy thin films with three different compositions (Pt66-Co34, Pt40-Co60 and Pt18-Co82) were deposited on Si(100) wafers and proposed as a set of certified reference materials (CRM) for the quantification and standardization of surface compositional analysis. The compositions of the binary alloy thin films were controlled by in-situ XPS analyses and the certified compositions of the films have been determined by ICP-AES and RBS analyses after thin film growth. Through comparison of the compositions determined by in-situ XPS with those by ICP, relatively accurate compositions could be obtained with a matrix effect correction. Standard deviations of XPS and AES round robin tests with the Pt-Co alloy thin films were large up to about 4%. On the other hand, the average compositions of the Pt-Co alloy thin films by two methods were in a good agreement within 1%. The formation of a Pt rich surface layer by ion beam sputtering indicates that the surface modification by preferential sputtering must be understood for a better compositional analysis.

• The Journal of Korean Society for Radiation Therapy
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• v.11 no.1
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• pp.6-10
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• 1999

The field size can be beam output, therefore MonitorUnit can be varied due to field size dependence The purpose of this study is to evaluate and compare the dose variation according to exchange of collimator The measurements were perfomed with Wellhofer dosimetry system(water phantom. ion chamber. electrometer. system controller. build up cap. etc)and two types of linear accerlerator (Mevatron KD, MevatronMX) Scatter can be affected to field size dependence and scatter correction is separated into collimator and phantom components, scatter components can affect by exchanging of collimator Measurements of collimator scatter factor(Sc) was done in air with build up cap. 1)Square field (5cm2 to 40cm2) was measured 2)and then keeping the upper jaw constant at loom and varing lower jaw from 5cm to 40cm, 3)keeping the lower jaw constant at 10cm and varing upper jaw from 5cm to 40cm Measurements of total scatter factor(Scp) was done in water at Dmax as the procedure of collimator scatter factor measurements in water Dmax The total scatter factors were obtained to the following equation(Sp=Scp/Sc) The measured data is normalized to the data of reference field size($10{\times}10$), rectangular field is inverted to equivalent field to compare three field size data As the collimator setting is varied, the output was changed In conclusion, the error was obtained small but it must be eliminated if we intend to reach the common stated goal of $5\%$ overall uncertainty in dose determination

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.381-396
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• 2020

Investigations of the commercial aircraft impact effect on nuclear island infrastructures have been drawing extensive attention, and this paper aims to perform the safety assessment of Generation III nuclear power plant (NPP) buildings subjected to typical commercial aircrafts crash. At present Part I, finite element (FE) models establishment and validations for both the aircrafts and NPP buildings are performed. (i) Airbus A320 and A380 aircrafts are selected as the representative medium and large commercial aircrafts, and the corresponding fine FE models including the skin, beam, fuel and etc. are established. By comparing the numerically derived impact force time-histories with the existing published literatures, the rationality of aircrafts models is verified. (ii) Fine FE model of the Chinese Zhejiang Sanao NPP buildings is established, including the detailed structures and reinforcing arrangement of both the containment and auxiliary buildings. (iii) By numerically reproducing the existing 1/7.5 scaled aircraft model impact tests on steel plate reinforced concrete (SC) panels and assessing the impact process and velocity time-history of aircraft model, as well as the damage and the maximum deflection of SC panels, the applicability of the existing three concrete constitutive models (i.e., K&C, Winfrith and CSC) are evaluated and the superiority of Winfrith model for SC panels under deformable missile impact is verified. The present work can provide beneficial reference for the integral aircraft crash analyses and structural damage assessment in the following two parts of this paper.