• The Journal of Korean Society for Radiation Therapy
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• 제10권1호
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• pp.97-101
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• 1998

In recent days, although many kinds of beam modifiers are developing and using for clinical purposes in accordance with progressing medical engineering, physical wedges are preferred to use as a beam modifier by a lot of institutions until now because of cost, complexities of dosimetry and mechanical uncertainties. According to progressing technology, available field size of wedge is more enlarger than that of old model LINAC. Because field size dependence of wedged fields increases in new model LINAC, we was trying to know that how much different PSFs are in enlarged wedged fields compared with open fields. In small or middle size of fields($4{\times}4{\sim}15{\times}15cm$), there are only a few percents of PSF variation between open and wedged fields. But there are $2{\sim}8\%\;variations\;in\;relatively\;large\;fields(20{\times}20{\sim}30{\times}40cm)$.

• Progress in Medical Physics
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• 제25권1호
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• pp.15-22
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• 2014

The IMRT is proper implement to get high dose deliver to tumor as its shape and selective approach in radiation therapy. Since the IMRT is performed as modulated the radiation fluence by the MLC created the open shapes and its irradiation time, the dose of segment of radiation field effects on the cumulated portal dose. The accurate output factor of small and step shape of segment is important to improve the determination of deliver tumor dose as it is directly proportional to dose. This experiment performed with the 6 MV photon beam of Clinac Ex(Varian) from $3{\times}3cm^2$ to $0.5{\times}0.5cm^2$ small field size for collimator jaw in MLC free and/or for MLC open field in fixed collimator jaw $10{\times}10cm^2$ using the CC01 ion chamber, SFD diode, diamond detector and X-Omat film dosimetry. As results of normalized to the reference field of $10{\times}10cm^2$ of MLC, the output factor of $3{\times}3cm^2$ showed $0.899{\pm}0.0106$, $0.855{\pm}0.0106$ for $2{\times}2cm^2$, $0.764{\pm}0.0082$ for $1{\times}1cm^2$ and $0.602{\pm}0.0399$ for $0.5{\times}0.5cm^2$. The output factor of MLC open field has shown a maximum 3.8% higher than that of the collimator jaw open field.

• Progress in Medical Physics
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• 제6권1호
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• pp.59-64
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• 1995

The aim of presentation is to obtain the beam parameters for tratment planning of steretactic radiosurgery. The dosimerical parameters such as TMR, scatter factor, and OAR was measured using diode, film, micro ion chamber, and thimble chanber for water phantom scanning. The results were compared each other. As a result, we determined OAR from film and scatter factor and TMR from diode as a basic data for treatment planning.

• Journal of Radiation Protection and Research
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• 제24권4호
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• pp.215-223
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• 1999

Characteristics of radiation field in the steam generator(S/G) water chamber of a PWR were investigated and the anticipated effective dose rates to the worker in the S/G chamber were evaluated by Monte Carlo simulation. The results of crud analysis in the S/G of the Kori nuclear power plant unit 1 were adopted for the source term. The MCNP4A code was used with the MIRD type anthropomorphic sex-specific mathematical phantoms for the calculation of effective doses. The radiation field intensity is dominated by downward rays, from the U-tube region, having approximate cosine distribution with respect to the polar angle. The effective dose rates to adults of nominal body size and of small body size(The phantom for a 15 year-old person was applied for this purpose) appeared to be 36.22 and 37.06 $mSvh^{-1}$) respectively, which implies that the body size effect is negligible. Meanwhile, the equivalent dose rates at three representative positions corresponding to head, chest and lower abdomen of the phantom, calculated using the estimated exposure rates, the energy spectrum and the conversion coefficients given in ICRU47, were 118, 71 and 57 $mSvh^{-1}$, respectively. This implies that the deep dose equivalent or the effective dose obtained from the personal dosimeter reading would be the over-estimate the effective dose by about two times. This justifies, with possible under- or over- response of the dosimeters to radiation of slant incidence, necessity of very careful planning and interpretation for the dosimetry of workers exposed to a non-regular radiation field of high intensity.

• The Journal of Korean Society for Radiation Therapy
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• 제11권1호
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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

• Progress in Medical Physics
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• 제20권4호
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• pp.260-268
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• 2009

In this study, we estimated inhomogeneity correction factor in small field. And, we evaluated accuracy of treatment planning and measurement data which applied inhomogeneity correction factor or not. We developed the Inhomogeneity Correction Phantom (ICP) for insertion of inhomogeneity materials. The inhomogeneity materials were 12 types in each different electron density. This phantom is able to adapt the EBT film and 0.125 cc ion chamber for measurement of dose distribution and point dose. We evaluated comparison of planning and measurement data using ICP. When we applied to inhomogeneity correction factor or not, the average difference was 1.63% and 10.05% in each plan and film measurement data. And, the average difference of dose distribution was 10.09% in each measurement film. And the average difference of point dose was 0.43% and 2.09% in each plan and measurement data. In conclusion, if we did not apply the inhomogeneity correction factor in small field, it shows more great difference in measurement data. The planning system using this study shows good result for correction of inhomogeneity materials. In radiosurgery using small field, we should be correct the inhomogeneity correction factor, more exactly.

• Progress in Medical Physics
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• 제15권2호
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• pp.59-62
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• 2004

We developed very small parallel plate radiation detector by using our existing experience of mating radiation dosimeter and capability of analyzing characteristics of dosimeter. The radiation detector was consisted of microfilm and carbon electrode. The detector was parallel plate type of all-filled ionization chamber. The ionization chamber had been fabricated using an acrylic plate for the air cavity and carbon coated microfilm for electrical configuration. The alr gap between two electrodes was 0.48 mm. The diameters of collect electrode and guard electrode were 3.3 mm, 5 mm respectively. The diameter of high voltage electrode was 5 mm. Nominal sensitive volume of the chamber was 0.016 ㎤. The major parameters of the chamber characteristics such as leakage current, reproducibility, dose rate effect, and polarity effect were measured. The experimental results were as followings. Leakage current was 0.1 pA. Standard deviation of reproducibility was less than 0.1%. Dose rate effect was less than 1.5%. Polarity effect was less than 2.4%. These data were comparable to those of commercially available dosimetric system for QA-purpose. As the result, we found that the radiation detector consisting of the ionization chamber, microfilm and carbon electrode, was satisfactory for the purpose of the small field dosimetry in size and characteristics. In the future, We will try to refine the dosimeter for use in very small volume.

• Radiation Oncology Journal
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• 제10권1호
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• pp.121-123
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• 1992

New measurement method for $S_{p}$ factors (Phantom Scatter Factors) is presented. The theoretical development of the approach is disscused showing that $S_{p}$ factors can be obtained from three measurements of ionnization in a blocked, reference field and open field. This method has been tested using $^{60}Co$ gamma rays. The results were within 1% deviation between the theory and the experiment for the $S_{p}$ factor. The new method does not need air measurement, and we could could determine the $S_P$ factors with a small piece of block

• Radiation Oncology Journal
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• 제11권1호
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• pp.175-181
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• 1993

Radiosurgery requires integral procedure where special devices and computer systems are needed for localization, dose planning and treatment. The aim of this work is to verify the overall mechanical accuracy of our LINAC and develop dose calculation algorithm for LINAC radiosurgery. The alignment of treatment machine and the performance testing of the entire system were extensively carried out and the basic data such as percent depth dose, off-axis ratio and output factor were measured. A three dimensional treatment planning system for stereotactic radiosurgery has been developed. We used an IBM personal computer with C programming language (IBM personal system/2, Model 80386, IBM Co., USA) for calculating the dose distribution. As a result, deviations at isocenter on gantry and table rotation for our treatment machine were acceptable since they were less than 2 mm. According to the phantom experiments, the focusing isocenter were successful by the error of less than 2 mm. Finally, the mechanical accuracy of our three dimensional planning system was confirmed by film dosimetry in sphere phantom.

• Journal of radiological science and technology
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• 제33권1호
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• pp.61-66
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• 2010

In this paper we evaluated small field dose characteristics of exclusive cone fields versus square fields for stereotactic radiosugery (SRS) which is based on linear accelerators (LINAC). For this test, we used a small beam detector (stereotactic fields detector : SFD) with a 6 MV photon beam and a water phantom system (IBA, Germany). Percentage depth dose (PDD) was measured for different field sets (cones : ${\Phi}1\;cm$, ${\Phi}2\;cm$, ${\Phi}3\;cm$ ; square fields : $1{\times}1\;cm^2$, $2{\times}2\;cm^2$, $3{\times}3\;cm^2$) at a source skin distance (SSD) of 100 cm. We measured the point depths at 1.5 cm, 5 cm, 10 cm, 20 cm, and 30 cm. The output factors were measured under the same geometrical conditions of the PDD and normalized at the maximum dose depth. To analyze the penumbra, we measured the dose profile with 95 cm of SSD, 5 cm of depth for each field sizes (${\Phi}1\;cm$, ${\Phi}3\;cm$, $1{\times}1\;cm^2$, and $3{\times}3\;cm^2$) using SFD. We obtained the values for every 1 mm interval in the physical field (90%) and 0.5 mm interval in the penumbra region (20 to 80%). The PDD variation of exclusive cones and square fields were 4.3 to 7.9% lesser than the standard field size ($10{\times}10\;cm^2$. The variation of PDD was reduced while the field size was increased. To compare the beam quality, we analyzed the $PDD_{20,10}$ and the results showed under the 1% of variations for all experiments except for ${\Phi}1\;cm$ cone and $1{\times}1\;cm^2$ fields. Output factors of exclusive cone were increased 3.1~4.6% than the square fields, and the penumbra region of exclusive cone was reduced 20% as compared to the square fields. As the previous researches report, it is very important for SRS and SFD that precise dosimetry in small beam fields. In this paper, we showed the effectiveness of exclusive cone, compared to square field. And we will study on the various detector characteristics for small beam fields.