• Progress in Medical Physics
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• v.14 no.1
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• pp.1-7
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• 2003

In this work we developed a EGS4 control code to calculate the dose distributions for high energy electron beams in water phantom applied longitudinal magnetic field. We reviewed the electron's motion in magnetic field and delivered equations for direction changs of the electron by the external magnetic field. The mathematical results are inserted into the EGS4 code system to account for the presence of external magnetic fields in phantom. The electron pencil beam paths of 6 MeV in water phantom are calculated for magnetic fields of 1-3 T and the dose distributions for a field of 1.0 cm in diameter are calculated for magnetic fields of 0.6-1 T using the code. From the results of path calculations we found that the lateral ranges of the electrons are reduced in the magnetic field of 3 T. For a field of 1 cm diameter and a magnetic field of 1 T, the small dose enhancement near the range of the electrons on the depth dose and the penumbra reduction of 0.15 cm on the beam profile are observed. We discussed and evaluated the results from the theoretical concepts.

• Journal of Radiation Protection and Research
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• v.24 no.1
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• pp.31-38
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• 1999

A real-time dose assessment system(FADAS : Following Accident Dose Assessment System) has been developed for the real-time accident consequence assessment against a nuclear accident. Field tracer experiment near Younggwang nuclear power plant was performed to improve the accuracy of developed system and to parameterize the site-specific parameters into the FADAS. The mean values and turbulent components of wind profile obtained through field experiment have been reflected to FADAS with site-specific conditions. The simulated results of diffusion model agreed well with the measured data through tracer experiment. The developed system is being used as a basic module of emergency preparedness system in Korea. The diffusion model which can be reflected site-specific parameters will be improved through field experiments continuously.

• Radiation Oncology Journal
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• v.17 no.3
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• pp.249-255
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• 1999

Purpose : The purpose of this study is to investigate fundamental aspects of the dose response of fluorescent screen-based electronic portal imaging devices (EPIDS). Materials and Methods : We acquired scanned signal across portal planes as we varied the radiation that entered the EPID by changing the thickness and anatomy of the phantom as well as the air gap between the phantom and the EPID. In addition, we simulated the relative contribution of the scintillation light signal in the EPID system. Results : We have shown that the dose profile across portal planes is a function of the air gap and phantom thickness. We have also found that depending on the density change within the phantom geometry, errors associated with dose response based on the EPID scan can be as high as $7\%$. We also found that scintillation light scattering within the EPID system is an important source of error. Conclusion : This study revealed and demonstrated fundamental characteristics of dose response of EPID, as relative to that of ion chambers. This study showed that EPID based on fluorescent screen cannot be an accurate dosimetry system.

• Imaging Science in Dentistry
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• v.37 no.1
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• pp.35-43
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• 2007

Purpose : To observe direct effect of irradiation on cariogenic Streptooccus mutans. Materials and Methods : S. mutans GS5 was exposed to irradiation with a single absorbed dose of 10, 20, 30, and 40Gy. Viability and changes in antibiotic sensitivity, morphology, transcription of virulence factors, and protein profile of bacterium after irradiation were examined by pour plate, disc diffusion method, transmission electron microscopy, RT-PCR, and SDS-PAGE, respectively. Results : After irradiation with 10 and 20Gy, viability of S. mutans was reduced. Further increase in irradiation dose, however, did not affect the viability of the remaining cells of S. mutans. Irradiated 5. mutans was found to have become sensitive to antibiotics. In particular, the bacterium irradiated with 40Gy increased its susceptibility to cefotaxime, penicillin, and tetracycline. Under the transmission electron microscope, number of morphologically abnormal cells was increased as the irradiation dose was increased. S. mutans irradiated with 10 Gy revealed a change in the cell wall and cell membrane. As irradiation dose was increased, a higher number of cells showed thickened cell wall and cell membrane and Iysis, and appearance of ghost cells was noticeable. In RT-PCR, no difference was detected in expression of gtfB and spap between cells with and without irradiation of 40Gy. In SDS-PAGE, proteins with higher molecular masses were gradually diminished as irradiation dose was increased. Conclusion : These results suggest that irradiation affects the cell Integrity of S. mutans, as observed by SDS-PAGE, and as manifested by the change in cell morphology, antibiotic sensitivity, and eventually viability of the bacterium.

• Journal of radiological science and technology
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• v.43 no.2
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• pp.105-114
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• 2020

This study aimed to assess of beam-matching accuracy for an 8 MV beam between the same model linear accelerators(Linac) commissioned over two years. Two models were got the customer acceptance procedure(CAP) criteria. For commissioning data for beam-matched linacs, the percentage depth doses(PDDs), beam profiles, output factors, multi-leaf collimator(MLC) leaf transmission factors, and the dosimetric leaf gap(DLG) were compared. In addition, the accuracy of beam matching was verified at phantom and patient levels. At phantom level, the point doses specified in TG-53 and TG-119 were compared to evaluate the accuracy of beam modelling. At patient level, the dose volume histogram(DVH) parameters and the delivery accuracy are evaluated on volumetric modulated arc therapy(VMAT) plan for 40 patients that included 20 lung and 20 brain cases. Ionization depth curve and dose profiles obtained in CAP showed a good level for beam matching between both Linacs. The variations in commissioning beam data, such as PDDs, beam profiles, output factors, TF, and DLG were all less than 1%. For the treatment plans of brain tumor and lung cancer, the average and maximum differences in evaluated DVH parameters for the planning target volume(PTV) and the organs at risk(OARs) were within 0.30% and 1.30%. Furthermore, all gamma passing rates for both beam-matched Linacs were higher than 98% for the 2%/2 mm criteria and 99% for the 2%/3 mm criteria. The overall variations in the beam data, as well as tests at phantom and patient levels remains all within the tolerance (1% difference) of clinical acceptability between beam-matched Linacs. Thus, we found an excellent dosimetric agreement to 8 MV beam characteristics for the same model Linacs.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.1
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• pp.1-9
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• 2004

Purpose : The aim of this study is to investigate the properties of small field size and to measure the penumbra and central axis depth dose varying to the jaw setting and off axis distance for indicate this data to small field sizes radiation therapy. Material and methods : The percentage depth dose, beam profile and central axis output dose was measured by farmer type ion chamber and pinpoint chamber using Primart linac with 6MV energy. Beam quality and penumbra variations according to the central axis shift, from center to every 2cm outside increment, and field size, from $1{\times}1cm$ to $10{\times}10cm$ was investigated and compared with that of the standard geometrical condition's results Results : The differences of measured values between two ion chamber was about $37\%$ at 10cm depth with $1{\times}1cm$ field sizes but as field size increased this differences was diminished gradually. Measured data from various off axis distance with the different asymmetric collimations are not changed significantly but as size decreased the dose variation was increased and at $1{\times}1cm$ field size dose difference among off axis distance was as much as $13\%$, and as shallower the measured depth the central axis dose variations among the OAD was increased, penumbra was not changed noticeably depending on off axis distance but the percentage of penumbra from its initial field sizes was strongly dependant on field sizes and penumbra occupation rates of its own field sizes ranging from $6\%$ at $10{\times}10cm$ to $50\%$ at $1{\times}1cm$ field size. Conclusion : For imrt treatment, there are several numbers of different gentry angles with beams of nonuniform fluences are required and several complex factors involved. Among them the characteristics of beam output varying to the geometrical setting and design of collimators are of important to attaining a good treatment results. As mentioned in results the differences of measured values are changed significantly depends on ion chamber volume, depths and field size. For providing quality radiation treatment, especially at small field size, those factor's should have considering deliberately.

• Progress in Medical Physics
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• v.10 no.2
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• pp.103-114
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• 1999

In this study, as a preliminary study for developing a full 3D photon dose calculation algorithm, We developed 2.5D photon dose calculation algorithm by extending 2D calculation algorithm to allow non-coplanar configurations of photon beams. For this purpose, we defined the 3d patient coordinate system and the 3d beam coordinate system, which are appropriate to 3d treatment planning and dose calculation. and then, calculate a transformation matrix between them. For dose calculation, we extended 2d "Clarkson-Cunningham" model to 3d one, which can calculate wedge fields as well as regular and irregular fields on arbitrary plane. The simple Batho's power-law method was implemented as an inhomogeneity correction. We evaluated the accuracy of our dose model following procedures of AAPM TG#23; radiation treatment planning dosimetry verifications for 4MV of Varian Clinac-4. As results, PDDs (percent depth dose) of cubic fields, the accuracy of calculation are within 1% except buildup region, and $\pm$3% for irregular fields and wedge fields. And for 45$^{\circ}$ oblique incident beam, the deviations between measurements and calculations are within $\pm$4%. In the case of inhomogeneity correction, the calculation underestimate 7% at the lung/water boundary and overestimate 3% at the bone/water boundary. At the conclusions, we found out our model can predict dose with 5% accuracy at the general condition. we expect our model can be used as a tool for educational and research purpose.. purpose..

• 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 Korean Society of Occupational and Environmental Hygiene
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• v.20 no.1
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• pp.29-40
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• 2010

This study was aimed at investigating the gene expression profile in basal ganglia of cadmium exposed rat based on cDNA array analysis. For cDNA array analysis, adult Sprague-Dawley male rats (350 ${\pm}$ 25 g) were intraperitoneally injected with 2.0 mg/kg body weight/day of CdCl2 (0.3 ml) for 5 days. For doserelated gene expression analysis rats were intraperitoneally injected with 0.0, 0.1, 0.3, 1.0 mg/kg body weight/day of CdCl$_2$ for 5 days. Control rats were injected with equal volume of saline. Cadmium concentration of brain was analyzed by atomic absorption spectrophotometer. For cDNA array, RNA samples were extracted from basal ganglia and reverse-transcribed in the presence of [${\alpha}$32P]-dATP. Membrane sets of the Atlas Rat 1.2 array II and Toxicology array 1.2 (Clontech, Palo Alto, CA) were hybridized with cDNA probe sets. RT-PCR was employed to validate the relative gene expression patterns obtained from the cDNA array. Northern blot hybridization methods were employed to assess the dose-related gene expression. Among the 2352 cDNAs, 671 genes were detected in both array sets and 63 genes of 38 classes showed significant (more than two fold) changes in expression. Thirty five of these genes were up-regulated and twenty eight were down-regulated in the cadmium exposed group. According to the dose-related gene expression analysis, heat shock 27 kDa protein (HSP27), neurodegeneration-associated protein 1 (Neurodap 1) genes were significantly up-regulated and melatonin receptor 1a (Mel1a), Kinesin family member 3C (KIF3C), novel kinesinrelated protein (KIF1D) genes were significantly downregulated even in the low-dose of cadmium exposed group (0.1 mg/kg body weight/day). Conclusions Sixty three genes detected in this study can give some more useful informations about the cadmium-induced neurotoxicity in the basal ganglia. As well as, HSP27, Neurodap1, Mel1a, KIF3C and KIF1D genes may be useful for the study of the cadmium-induced neurotoxicity because these genes showed dramatic changes of mRNA levels in response to the low dose of cadmium exposure.

• Progress in Medical Physics
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• v.29 no.3
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• pp.92-100
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• 2018

The manufacturer of a linear accelerator (LINAC) has reported that the target melting phenomenon could be caused by a non-recommended output setting and the excessive use of monitor unit (MU) with intensity-modulated radiation therapy (IMRT). Due to these reasons, we observed an unexpected beam interruption during the treatment of a patient in our institution. The target status was inspected and a replacement of the target was determined. After the target replacement, the beam profile was adjusted to the machine commissioning beam data, and the absolute doses-to-water for 6 MV and 10 MV photon beams were calibrated according to American Association of Physicists in Medicine (AAPM) Task Group (TG)-51 protocol. To verify the beam data after target replacement, the beam flatness, symmetry, output factor, and percent depth dose (PDD) were measured and compared with the commissioning data. The difference between the referenced and measured data for flatness and symmetry exhibited a coincidence within 0.3% for both 6 MV and 10 MV, and the difference of the PDD at 10 cm depth ($PDD_{10}$) was also within 0.3% for both photon energies. Also, patient-specific quality assurances (QAs) were performed with gamma analysis using a 2-D diode and ion chamber array detector for eight patients. The average gamma passing rates for all patients for the relative dose distribution was $99.1%{\pm}1.0%$, and those for absolute dose distribution was $97.2%{\pm}2.7%$, which means the gamma analysis results were all clinically acceptable. In this study, we recommend that the beam characteristics, such as beam profile, depth dose, and output factors, should be examined. Further, patient-specific QAs should be performed to verify the changes in the overall beam delivery system when a target replacement is inevitable; although it is more important to check the beam output in a daily routine.