• Progress in Medical Physics
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• v.17 no.1
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• pp.17-23
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• 2006

In Vivo dosimetry is a method to evaluate the radiotherapy; it is used to find the dosimetric and mechanical errors of radiotherapy unit. In this study, on-line In Vivo dosimetry was enabled by measuring the skin dose with MOSFET detectors attached to patient's skin during treatment. MOSFET dosimeters were found to be reproducible and independent on beam directions. MOSFET detectors were positioned on patient's skin underneath of the dose build-up material which was used to minimize dosimetric error. Delivered dose calculated by the plan verification function embedded in the radiotherapy treatment planning system (RTPs), was compared with measured data point by point. The dependency of MOSFET detector used in this study for energy and dose rate agrees with the specification provided by manufacturer within 2% error. Comparing the measured and the calculated point doses of each patient, discrepancy was within 5%. It was enabled to verify the IMRT by using MOSFET detector. However, skin dosimetry using conventional ion chamber and diode detector is limited to the simple radiotherapy.

• Progress in Medical Physics
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• v.32 no.4
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• pp.99-106
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• 2021

Purpose: In this study, we aimed to manufacture a patient-specific gel phantom combining three-dimensional (3D) printing and polymer gel and evaluate the radiation dose and dose profile using gel dosimetry. Methods: The patient-specific head phantom was manufactured based on the patient's computed tomography (CT) scan data to create an anatomically replicated phantom; this was then produced using a ColorJet 3D printer. A 3D polymer gel dosimeter called RTgel-100 is contained inside the 3D printing head phantom, and irradiation was performed using a 6 MV LINAC (Varian Clinac) X-ray beam, a linear accelerator for treatment. The irradiated phantom was scanned using magnetic resonance imaging (Siemens) with a magnetic field of 3 Tesla (3T) of the Korea Institute of Nuclear Medicine, and then compared the irradiated head phantom with the dose calculated by the patient's treatment planning system (TPS). Results: The comparison between the Hounsfield unit (HU) values of the CT image of the patient and those of the phantom revealed that they were almost similar. The electron density value of the patient's bone and brain was 996±167 HU and 58±15 HU, respectively, and that of the head phantom bone and brain material was 986±25 HU and 45±17 HU, respectively. The comparison of the data of TPS and 3D gel revealed that the difference in gamma index was 2%/2 mm and the passing rate was within 95%. Conclusions: 3D printing allows us to manufacture variable density phantoms for patient-specific dosimetric quality assurance (DQA), develop a customized body phantom of the patient in the future, and perform a patient-specific dosimetry with film, ion chamber, gel, and so on.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.6
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• pp.268-273
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• 2014

$Y_2O_3$ ceramic specimens were fabricated from the granular powder, obtained by spray drying process from the slurry. The slurry was prepared by mixing PVA binder, NaOH for Ph control, PEG and $Y_2O_3$ powder. The $Y_2O_3$ specimen was shaped in size of ${\phi}14mm$ and then sintered at $1650^{\circ}C$. The characteristics, microstructure, densities and plasma resistance of the $Y_2O_3$ specimens were investigated with the function of forming pressure and sintering time. $Y_2O_3$ specimens were exposed under the $CHF_3/O_2/Ar$ plasma, the dry etching treatment of specimens was carried out by the physical reaction etching of $Ar^+$ ion beam and the chemical reaction etching of $F^-$ ion decomposed from $CHF_3$. With increasing sintering time, $Y_2O_3$ specimens showed relatively high density and strong resistance in plasma etching test.

• Journal of radiological science and technology
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• v.39 no.4
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• pp.571-575
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• 2016

Monte Carlo simulations are widely used as the most accurate technique for dose calculation in radiation therapy. In this paper, the GATE6(Geant4 Application for Tomographic Emission ver.6) code was employed to calculate the dosimetric performance of the photon beams from a linear accelerator(LINAC). The treatment head of a Varian 21EX Clinac was modeled including the major geometric structures within the beam path such as a target, a primary collimator, a flattening filter, a ion chamber, and jaws. The 6 MV photon spectra were characterized in a standard $10{\times}10cm^2$ field at 100 cm source-to-surface distance(SSD) and subsequent dose estimations were made in a water phantom. The measurements of percentage depth dose and dose profiles were performed with 3D water phantom and the simulated data was compared to measured reference data. The simulated results agreed very well with the measured data. It has been found that the GATE6 code is an effective tool for dose optimization in radiotherapy applications.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.77-77
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• 2017

Titanium and its alloys offer attractive properties in a variety of applications. These are widely used for the field of biomedical implants because of its good biocompatibility and high corrosion resistance. Titanium anodizing is often used in the metal finishing of products, especially those can be used in the medical devices with dense oxide surface. Based on SAE/AMS (Society of Automotive Engineers/Aerospace Material Specification) 2488D, it has the specification for industrial titanium anodizing that have three different types of titanium anodization as following: Type I is used as a coating for elevated temperature forming; Type II is used as an anti-galling coating without additional lubrication or as a pre-treatment for improving adherence of film lubricants; Type III is used as a treatment to produce a spectrum of surface colours on titanium. In this study, we have focused on Type II anodization for the medical (dental and orthopedic) application, the anodized surface was modified with gray color under alkaline electrolyte. The surface characteristics were analyzed with Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM), surface roughness, Vickers hardness, three point bending test, biocompatibility, and corrosion (potentiodynamic) test. The Ti-6Al-4V alloy was used for specimen, the anodizing procedure was conducted in alkaline solution (NaOH based, pH>13). Applied voltage was range between 20 V to 40 V until the ampere to be zero. As results, the surface characteristics of anodic oxide layer were analyzed with SEM, the dissecting layer was fabricated with FIB method prior to analyze surface. The surface roughness was measured by arithmetic mean deviation of the roughness profile (Ra). The Vickers hardness was obtained with Vickers hardness tester, indentation was repeated for 5 times on each sample, and the three point bending property was verified by yield load values. In order to determine the corrosion resistance for the corrosion rate, the potentiodynamic test was performed for each specimen. The biological safety assessment was analyzed by cytotoxic and pyrogen test. Through FIB feature of anodic surfaces, the thickness of oxide layer was 1.1 um. The surface roughness, Vickers hardness, bending yield, and corrosion resistance of the anodized specimen were shown higher value than those of non-treated specimen. Also we could verify that there was no significant issues from cytotoxicity and pyrogen test.

• Journal of the Korean Magnetics Society
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• v.19 no.6
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• pp.197-202
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• 2009

The property of soft magnetism for the Corning glass/non-buffer or buffer Ta/Conetic(NiFeCuMo)/Ta prepared by the ion beam deposition sputtering was studied. The effect of crystal property and post annealing treatment depending on the thickness of Conetic thin films was investigated. The coercivities of Conetic thin films with easy and hard direction along to the applying magnetic field during deposition were compared with each other. The coercivity and magnetic susceptibility of Ta(5 nm)/Conetic(50 nm) thin film were 0.12 Oe and 1.2 ${\times}\;10^4$, respectively. From these results, firstly, the Conetic thin film was more soft magnetism thin film than other one such as permalloy NiFe. Secondly, the usage of soft magnetism Conetic thin film for GMR-SV (giant magneoresistance-spin valve) or MTJ (Megnetic Tunnel Junction) structure in a low magnetic field can be possible.

• Radiation Oncology Journal
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• v.19 no.1
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• pp.74-80
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• 2001

Purpose : Irradiation cones by using backscatter electrons are made for the treatment of superficial small lesions of skin, oral cavity, and rectum where a significant dose gradient and maximum surface dose is desired. Methods and Materials : Backscatter electrons are produced from the primary electron beams from the linear accelerators. The design consists of a cylindrical cone that has a thick circular plate of high atomic number medium (Pb or Cu) attached to the distal end, and the plate can be adjusted the reflected angle. Primary electrons strike the metal plate perpendicularly and produce backscatter electrons that reflect through the lateral hole for treatment. Using film and a parallel plate ion chamber, backscatter electron dose characteristics are measured. Results : The depth dose characteristic of the backscatter electron is very similar to that of the hard x-ray beam that is commonly used for the intracavitary and superficial lesions. The basckscatter electron energy is nearly constant and effectively about 1.5 MeV from the clinical megavoltage beams. The backscatter electron dose rate of $35\~85\;cGy/min$ could be achieved from modern accelerators without any modification. and the depth in water of $50\%$ depth dose from backscatter electron located at 6mm for $45^{\circ}$ angled lead scatter. The beam flatness is dependent on the slit size and the depth of treatment, but is satisfactory to treat small lesions. Conclusions : The measured data for backscatter electron energy, depth dose flatness dose rate and absolute dose indicates that the backscatter electrons are suitable for clinical use.

• The Journal of Korean Society for Radiation Therapy
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• v.31 no.1
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• pp.17-24
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• 2019

Purpose: The present study aims to assess the level of coherency and the accuracy of Point dose of the Isocenter of VERO, a linear accelerator developed for the purpose of the Stereotactic Body Radiation Therapy(SBRT). Materials and Method: The study was conducted randomly with 10 treatment plans among SBRT patients in Kyungpook National University Chilgok Hospital, using VERO, a linear accelerator between June and December, 2018. In order to assess the equipment's power stability level, we measured the output constancy by using PTW-LinaCheck, an output detector. We also attempted to measure the level of accuracy of the equipment's Laser, kV(Kilo Voltage) imaging System, and MV(Mega Voltage) Beam by using Tofu Phantom(BrainLab, Germany) to assess the accuracy level of geometrical Isocenter. We conducted a comparative analysis to assess the accuracy level of the dose by using an acrylic Phantom($30{\times}30{\times}20cm$), a calibrated ion chamber CC-01(IBA Dosimetry), and an Electrometer(IBA, Dosimetry). Results: The output uniformity of VERO was calculated to be 0.66 %. As for geometrical Isocenter accuracy, we analyzed the error values of ball Isocenter of inner Phantom, and the results showed a maximum of 0.4 mm, a minimum of 0.0 mm, and an average of 0.28 mm on X-axis, and a maximum of -0.4 mm, a minimum of 0.0 mm, and an average of -0.24 mm on Y-axis. A comparison and evaluation of the treatment plan dose with the actual measured dose resulted in a maximum of 0.97 % and a minimum of 0.08 %. Conclusion: The equipment's average output dose was calculated to be 0.66 %, meeting the ${\pm}3%$ tolerance, which was considered as a much uniform fashion. As for the accuracy assessment of the geometric Isocenter, the results met the recommended criteria of ${\pm}1mm$ tolerance, affirming a high level of reproducibility of the patient's posture. The difference between the treatment plan dose and the actual measurement dose was calculated to be 0.52 % on average, significantly less than the 3 % tolerance, confirming that it obtained predicted does. The current study suggested that VERO equipment is suitable for SBRT, and would result in notable therapeutic effect.

• Journal of radiological science and technology
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• v.35 no.3
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• pp.265-273
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• 2012

Aquisition of accurate beam data is very important to calculate a reliable dose distribution of the treatment planning system for small radiation fields in intensity-modulated radiation therapy(IMRT) and stereotactic radiosurgery(SRS). For the measurement of small fields, the choice of a suitable detector is important due to the shape gradient in profile penumbra, the lack of lateral electronic equilibrium, and the effect of effective detector volume. Therefore, this study was to analyze the dosimetric characteristics of various detectors in measurement of beam data for small fields of linear accelerator. 0.01cc and 0.13cc ion chambers (CC01 and CC13) and a stereotactic diode detector(SFD) were used for measurement of small fields. The beam data, including the percent depth dose, output factor, and beam profile were acquired under 6 MV and 15 MV photon beams. Measurements were performed with the field size ranging from $2{\times}2cm^2$ to $5{\times}5cm^2$. For $2{\times}2cm^2$ field size, the differences of the ratios of $PDD_{20}$ and $PDD_{10}$ measured by CC01 and SFD detectors were 1.02% and 0.12% for 6 MV and 15 MV photon beams, respectively. For field sizes larger than $3{\times}3cm^2$, the differences of values of $PDD_{20}/PDD_{10}$ obtained from each detector were 1.15% and 0.71% for 6 MV and 15 MV photon beams, respectively. The output factors obtained from CC01 and SFD for $2{\times}2cm^2$ field size were within 0.5% and 1.5% for 6 MV and 15 MV, respectively. The differences in output factor of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes were within 0.5%. Profile penumbras measured by the SFD, CC01, and CC13 detectors at three depths were average 2.7 mm and 3.5 mm, 3.4 mm and 4.3 mm, and 5.2 mm and 6.1 mm for 6 MV and 15 MV photon beams, respectively. In conclusion, it could be possible to use of the CC01 and SFD detectors for the measurement of percent depth dose and output factor for $2{\times}2cm^2$ field size, and to use of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes. CC01 and SFD detectors, consider ably smaller than the radiation field, should be used in order to accurately measure the profile penumbra for small field sizes.

• The Journal of Korean Society for Radiation Therapy
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• v.11 no.1
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• pp.16-21
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• 1999

Purpose : The aim of this study is to conform the possibility of the liquid type EPID as a QC tools to clinical indication and of replacement of the film dosimetry. Aditional aim is to describe a procedure for the use of a EPID as a physics calibration tool in the measurements of radiation beam parameters which are typically carried out with film. Method & Materials : In this study we used the Clinac 2100c/d with EPID. This system contains 65536 liquid-filled ion chambers arranged in a $256{\times}256$ matrix and the imaging area is $32.5{\times}32.5cm$ with liquid layer thickness of 1mm. The EPID was tested for different field sizes under typical clinical conditions and pixel values were calibrated against dose by producing images using various thickness of lead attenuators(lead step wedge) using 6 & 10MV x-ray. We placed various thickness of lead on the table of linear accelerator and set the portal vision an SDD of 100cm. To acquire portal image we change the field size and energy, and we recorded the average pixel value in a $3{\times}3$ pixel region of interest(ROI) at field center was recorded. The pixel values were also measured for different field sizes in order to evaluate the dependence of pixel value on x-ray energy spectrum and various scatter components. Result : The EPID, as a whole, was useful as a QA tool and dosimetry device. In mechanical check, cross-hair centering was well matched and the error was less than ?2mm and light/radiation field coincidence was less than 1mm also. In portal dosimetry the wider the field size the the higher the pixel value and as the lead thickness increase, the pixel value was exponentially decreased. Conclusions : The EPID was very suitable for QA tools and it can be used to measure exit dose during patients treatment with reasonable accuracy. But when indicate the EPID to clincal study deep consideration required