• The Journal of Korean Society for Radiation Therapy
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• v.7 no.1
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• pp.15-31
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• 1995

The radiosurgery treatment is one time, non surgical approach to the treatment of patients with intracranial disorders whose conditions would be difficult or dangerous to treat with conventional sugical procedures. The LINAC based radiosurgery is based on the combination of multiple isocentric arc irradiation with small fields centered in the stereotactic target. The absorption of the beam in a tissue equivalent medium, such as water, as well as the uniformity, or profile, of the beam must be precisely documented. The beam characteristics and dosimetric measurememts of the 6MV X-ray beam from a ML-6M linear accelerator are examined. The percent depth dose (PDD) and beam profile (including flatness, symmetry and penumbra) is calibrated with the radiosurgery cone in water phantom. The cone is made of lead which size is from $10{\times}10mm{\phi}$ to $30{\times}30mm{\phi}$ All of these dosimetric measurements sufficiently characterized the beam to permit safe clinical use.

• Radiation Oncology Journal
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• v.18 no.1
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• pp.51-58
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• 2000

Purpose :The effect of PTK inhibitors (herbimycin A and genistein) on the induction of radiation-induced apoptosis in Ph-positive KS62 leukemia cell line was investigated. Materials and Methods :K562 cells in exponential growth phase were irradiated with a linear accelerator at room temperature. For 6 MV X-ray irradiation and drug treatment, cultures were initiated at 2×106 cells/mL. The cells were irradiated with 10 Gy. Stock solutions of herbimycin A and genistein were prepared in dimethyl sulphoxide (DMSO). After incubation at 37$^{\circ}C$ for 0$\~$48 h, the extent of apoptosis was determined using agarose gel electrophoresis and TUNEL assay. The progression of cells through the cell cycle after irradiation and drug treatment was also determined with flow cytometry. Western blot analysis was used to monitor bel-2, bel-X$_{L}$ and bax protein levels. Results :Treatment with 10 Gy X-irradiation did not result in the induction of apoptosis. The HMA alone (500 nM) also failed to induce apoptosis. By contrast, incubation of K562 cells with HMA after irradiation resulted in a substantial induction of nuclear condensation and fragmentation by agarose gel electro-phoresis and TUNEL assay. Genistein failed to enhance the ability of X-irradiation to induce DNA fragmentation. Enhancement of apoptosis by HMA was not attributable to downregulation of the bel-2 or bel-X$_{L}$ anti-apoptotic proteins. When the cells were irradiated and maintained with HMA, the percentage of cells in G2/M phase decreased to 30$\~$40$\%$ at 48 h. On the other hand, cells exposed to 10 Gy X-irradiation alone or maintained with genistein did not show marked cell cycle redistribution. Conclusion : We have shown that nanomolar concentrations of the PTK inhibitor HMA synergize with X-irradiation in inducing the apoptosis in Ph (+) K562 leukemia cell line. While, genistein, a PTK inhibitor which is not selective for p210$^{bcr/abl}$ failed to enhance the radiation induced apoptosis in KS62 cells. It is unlikely that the ability of HMA to enhance apoptosis in K562 cells is attributable to bel-2 family. It is plausible that the relationship between cell cycle delays and cell death is essential for drug development based on molecular targeting designed to modify radiation-induced apoptosis.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.89-96
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• 2006

Purpose: To study effectiveness of heterogeneity correction of internal-body inhomogeneities and patient positioning immobilizers in dose calculation, using images obtained from CT-Simulator. Materials and Methods: A water phantom($250{\times}250{\times}250mm^3$) was fabricated and, to simulate various inhomogeneity, 1) bone 2) metal 3) contrast media 4) immobilization devices(Head holder/pillow/Vac-lok) were inserted in it. And then, CT scans were peformed. The CT-images were input to Radiation Treatment Planning System(RTPS) and the MUs, to give 100 cGy at 10 cm depth with isocentric standard setup(Field Size=$10{\times}10cm^2$, SAD=100 cm), were calculated for various energies(4, 6, 10 MV X-ray). The calculated MUs based on various CT-images of inhomogeneities were compared and analyzed. Results: Heterogeneity correction factors were compared for different materials. The correction factors were $2.7{\sim}5.3%$ for bone, $2.7{\sim}3.8%$ for metal materials, $0.9{\sim}2.3%$ for contrast media, $0.9{\sim}2.3%$ for Head-holder, $3.5{\sim}6.9%$ for Head holder+pillow, and $0.9{\sim}1.5%$ for Vac-lok. Conclusion: It is revealed that the heterogeneity correction factor calculated from internal-body inhomogeneities have various values and have no consistency. and with increasing number of beam ports, the differences can be reduced to under 1%, so, it can be disregarded. On the other hand, heterogeneity correction from immobilizers must be regarded enough to minimize inaccuracy of dose calculation.

• Journal of radiological science and technology
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• v.39 no.2
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• pp.177-184
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• 2016

Recently linear accelerator of radiation therapy intensity modulated radiation therapy, stereotactic radiation therapy are widely used. Such radiation treatment techniques are generally difficult to exclude the small field by using the inverse treatment plan. It is necessary to dose an accurate measurement of characteristics of the small field. Thus, using different detectors to measure the volume of the effective percentage depth dose, beam profile, and the output factor of the small field was to evaluate the dose characteristics of each detector. Experimental results for the X-ray beam 6 MV energy beam quality($PDD_{20}/PDD_{10}$) is $10{\times}10cm^2$ Diode detector is as high as 2.4% compared to Pinpoint detector. All field size to lesser effective volume of Diode detector shows that it is far better than other detectors by more than 50% of small penumbra, therefore spatial resolution far excellent. In field size $2{\times}2cm^2$ Semiflex detector was measured about 2% less than the other detector. Field size $1{\times}1cm^2$ is that there is no judgment about the validity show the difference between 20%. Field size $1{\times}1cm^2$ from the measured values of the Diode detector and Pinpoint detector showed a 13% difference. Less than field size $3{\times}3cm^2$ the feed to the difference between the output factor of the effective volume of the detector to be used for the effective volume available to the detector.

• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.985-991
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• 2023

A tissue-equivalent phantom is necessary for quality control of hyperthermia therapy. However, since there is no phantom for this purpose, phantoms made from agar are being used in various studies. The tissue-equivalent properties of the agar phantom were confirmed by comparison with the tissue-equivalent material bolus in this study. CT images of the agar phantom and bolus were acquired, and tissue equivalent characteristics were analyzed with image analysis and dose calculation using a computerized radiation therapy planning system. The average pixel value was 96.960±10.999 in bolus, 108.559±8.233 in 3% agar phantom, and 111.844±8.651 in 4% agar phantom. Using the SSD technique, 100 cGy was prescribed at a depth of 1.5 cm and 6 MV X -ray was set to irradiated to 10x10 cm2, and the absorbed dose according to depth was calculated from the central axis of the beam. The intraclass correlation coefficient of dose distribution of bolus, 3% agar phantom, and 4% agar phantom was 0.979 (p<.001, 95%CI .957-.991). The density (g/cm3) at the point where the absorbed dose was calculated was 0.990±0.020 at the bolus, 1.018±0.020 at the 3% agar phantom, and 1.035±0.024 at the 4% agar phantom. In this study, the internal density distribution and uniformity of the agar phantom were confirmed to be appropriate as a tissue equivalent material by analysis of CT images and a computerized radiation therapy planning system.

• Radiation Oncology Journal
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• v.3 no.2
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• pp.145-151
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• 1985

The peripheral dose distributions of wedge fields of Co-60 $\gamma-ray$ and 1 OMV x-ray were measured by the solid state detector controlled by means of semiautomatic water phentom system. The measurements were made on the principal plane parallel to the cross section of wedge filter (blade and ridge direction). For parallel motion of the detector to the beam axis the distance from the margin of radiation field at suface were 3, 5 and 10cm. For tranverse motion the depth of measurement were dm, 5, 10 and 15cm. The followings were drawn from the measurement. 1. The peripheral dose of the blade side of wedges was generally higher than that of the ridge side at symmetric point about beam axis. 2. In the superficial region phenomena of dose build-up appeared. 3. For Co-60 $\gamma-ray$ field, the peripheral dose did not monotonously decrease with the distance from the field margin but increase in some range, consequently showing a peak dose. 4. The peripheral dose did not only depend on radiation quality and field size, but also on wedge angle and wedge direction.

• Progress in Medical Physics
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• v.13 no.1
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• pp.1-8
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• 2002

Accurate knowledge of the distribution of contamination electrons ( which comes from mainly gantry head by Compton scattering, pair production, and tray: henceforth called leptons ) at the surface and in the first centimeters of tissue is essential for the clinical practice of radiation oncology. Such lepton tends to reduce or eliminate the ‘skin-sparing’ advantage of megavoltage photon beam radiotherapy, This information is needed to prescribe a absorbed dose to a skin volume at a few millimeter depth in high energy therapeutic radiation photon beam All experiments were done with 15 MV photon beam from a dual energy linear accelerator (Clinac 1800, Varian). Field size is defined by ranged from 10.0$\times$10.0 to 30.0$\times$30.0 $\textrm{cm}^2$. The absorbed dose and distribution of leptons in therapeutic radiation beam (15 MV) are investigated by means of variable blocked beams of 30.0$\times$30.0 $\textrm{cm}^2$ and dose beam profiles partly removed leptons with a copper plate. A numerous leptons mainly are distributed as shape of broad cone in the central photon beam and leptons path length in the water are shorter than 2.5 cm because of the leptons energy having around 3.0 MeV. These results clearly appears that the subtraction of leptons from the total depth dose curve not only lower the absolute dose in the buildup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth.

• Radiation Oncology Journal
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• v.20 no.4
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• pp.391-395
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• 2002

Purpose : To confirm the accuracy of the radiation dose at the isocenter by the standard linear accelerator-based stereotactic radiosurgery technique which was developed at Seoul National University Hospital. Materials and Methods : Radiation dosimetry was undertaken during standard 5-arc radiosurgery using 6 MV X-ray beam from CL2100C linac. The treatment head was attached with circular tertiary collimators of 10 and 20 mm diameter. We measured the absorbed dose at the isocenter of a multi-purpose phantom using two kinds of detector : a 0.125 co ionization chamber and a silicon diode detector. Results : The dose differences at each arc plane between the planned dose and the measured dose at the isocenter raged from $-0.73\%\;to\;-2.69\%$ with the 0.125 cc ion chamber, and from $-1.29\%\;to\;-2.91\%$ with the diode detector during radiosurgery with the tertiary collimator of 20 mm diameter. Those with the 10-mm tertiary collimator ranged from $-2.39\%\;to\;-4.25\%$ with the diode. Conclusion : The dose accuracy at the isocenter was ${\pm}3\%$. Therefore, further efforts such ws modification in processing of the archived image through DICOM3.0 format are required to lessen the dose difference.

• The Korean Journal of Food & Health Convergence
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• v.4 no.1
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• pp.15-22
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• 2018

A radiation dosimeter is important to assess quality assurance (QA) of radiation therapy devices and to estimate the radiation dose in vivo dosimetry. Recently, optically stimulated luminescence detector (OSLD) is widely used in clinical filed. Therefore, the purpose of this study is to evaluate dose, energy, and angular dependence of OSLD and EBT3 film. The absorbed dose in clinical linear accelerator (Linac) beam is calibrated for dose per monitor unit (MU). Dose, energy, and angular dependence of OSLD and EBT3 film are estimated after the calibration procedure. The absorbed dose is measured at 50, 100, 150, and 200 cGy in an 6 MV X-ray beam for dose dependence. A dose of 150 cGy is delivered to OSLD and EBT3 film with 6 and 10 MV photon energies for energy dependence. For measurements of angular dependence, angular positions of gantry are $0^{\circ}{\pm}80^{\circ}$ with 6 MV at 150 cGy. The results of dose dependence is linear for OSLD and EBT3 film. For the results of energy dependence, errors were 0.39% and 0.03% for OSLD and EBT3 film, respectively. The results of dose for angular is decreased from $0^{\circ}$ to ${\pm}80^{\circ}$ for both OSLD and EBT3 film. When angle of $0^{\circ}$ is normalized to 1, and the dose is decreased to 60 and 66% at $80^{\circ}$ for OSLD and EBT3 film, respectively. Dose and energy dependence of OSLD and EBT3 film are measured within the recommendation of manufacturer. Angular dependence is increased from $0^{\circ}$ to ${\pm}80^{\circ}$ for OSLD and EBT3 film. The characteristics of OSLD and EBT3 film are similar and expected to useful for clinical field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.11
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• pp.816-820
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• 2013

We investigated the characteristics of the silicon oxy-nitride and nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) at the low temperature with a varying $NH_3/N_2O$ mixing ratio and a fixed $SiH_4$ flow rate. The deposition temperature was held at $150^{\circ}C$ which was the temperature compatible with the plastic substrate. The composition and bonding structure of the nitride films were investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Nitrogen richness was confirmed with increasing optical band gap and increasing dielectric constant with the higher $NH_3$ fraction. The leakage current density of the nitride films with a high NH3 fraction decreased from $8{\times}10^{-9}$ to $9{\times}10^{-11}(A/cm^2$ at 1.5 MV/cm). This results showed that the films had improved electrical properties and could be acceptable as a gate insulator for thin film transistors by deposited with variable $NH_3/N_2O$ mixing ratio.