• Journal of Radiation Protection and Research
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• v.36 no.3
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• pp.127-133
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• 2011

In 2007, the International Commission on Radiological Protection (ICRP) published Recommendations of the International Commission on Radiological Protection. Accordingly IAEA safety standards committees have reviewed and revised the BSS. The process of the implementation of the ICRP 103 into Korean radiation protection regulations has been continued. Although the new recommendations retain the fundamental protection principles, the impact of the new ICRP recommendations will necessarily be greater than ever before. ICRP recommends the application of dose constraint in planned situations and reference level in existing & emergency situations for strengthening of the principle of optimization. Dose constraints and reference level play a criterion on the level of individual dose as prospective and source-related values. Therefore it is necessary to apply dose constraints and reference levels to all nuclear and RI&RG facilities in Rep. of Korea. Dose constraints and reference level of occupational exposure will be set-up by the stakeholder itself with the cooperation of regulatory body. In this study, the implementation method was discussed to apply the dose constraints and reference level as the procedure for the optimization, not the tool of the regulation.

• Progress in Medical Physics
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• v.23 no.1
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• pp.15-25
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• 2012

The aim of this study is to evaluate plan quality and dose accuracy for Volumetric Modulated Arc Therapy (VMAT) on the TG-119 and is to investigate the effects on variation of the selectable optimization parameters of VMAT. VMAT treatment planning was implemented on a Varian iX linear accelerator with ARIA record and verify system (Varian Mecical System Palo Alto, CA) and Oncentra MasterPlan treatment planning system (Nucletron BV, Veenendaal, Netherlands). Plan quality and dosimetric accuracy were evaluated by effect of varying a number of arc, gantry spacing and delivery time for the test geometries provided in TG-119. Plan quality for the target and OAR was evaluated by the mean value and the standard deviation of the Dose Volume Histograms (DVHs). The ionization chamber and $Delta^{4PT}$ bi-planar diode array were used for the dose evaluation. For treatment planning evaluation, all structure sets closed to the goals in the case of single arc, except for the C-shape (hard), and all structure sets achieved the goals in the case of dual arc, except for C-shape (hard). For the variation of a number of arc, the simple structure such as a prostate did not have the difference between single arc and dual arc, whereas the complex structure such as a head and neck showed a superior result in the case of dual arc. The dose distribution with gantry spacing of $4^{\circ}$ was shown better plan quality than the gantry spacing of $6^{\circ}$, but was similar results compared with gantry spacing of $2^{\circ}$. For the verification of dose accuracy with single arc and dual arc, the mean value of a relative error between measured and calculated value were within 3% and 4% for point dose and confidence limit values, respectively. For the verification on dose accuracy with the gantry intervals of $2^{\circ}$, $4^{\circ}$ and $6^{\circ}$, the mean values of relative error were within 3% and 5% for point dose and confidence limit values, respectively. In the verification of dose distribution with $Delta^{4PT}$ bi-planar diode array, gamma passing rate was $98.72{\pm}1.52%$ and $98.3{\pm}1.5%$ for single arc and dual arc, respectively. The confidence limit values were within 4%. The smaller the gantry spacing, the more accuracy results were shown. In this study, we performed the VMAT QA based on TG-119 procedure, and demonstrated that all structure sets were satisfied with acceptance criteria. And also, the results for the selective optimization variables informed the importance of selection for the suitable variables according to the clinical cases.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.380-387
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• 2015

A lead slowing-down spectrometer (LSDS) system is a promising nondestructive assay technique that enables a quantitative measurement of the isotopic contents of major fissile isotopes in spent nuclear fuel and its pyroprocessing counterparts, such as $^{235}U$, $^{239}Pu$, $^{241}Pu$, and, potentially, minor actinides. The LSDS system currently under development at the Korea Atomic Energy Research Institute (Daejeon, Korea) is planned to utilize a high-flux ($>10^{12}n/cm^2{\cdot}s$) neutron source comprised of a high-energy (30 MeV)/high-current (~2 A) electron beam and a heavy metal target, which results in a very intense and complex radiation field for the facility, thus demanding structural shielding to guarantee the safety. Optimization of the structural shielding design was conducted using MCNPX for neutron dose rate evaluation of several representative hypothetical designs. In order to satisfy the construction cost and neutron attenuation capability of the facility, while simultaneously achieving the aimed dose rate limit (< $0.06{\mu}Sv/h$), a few shielding materials [high-density polyethylene (HDPE)eBorax, $B_4C$, and $Li_2CO_3$] were considered for the main neutron absorber layer, which is encapsulated within the double-sided concrete wall. The MCNP simulation indicated that HDPE-Borax is the most efficient among the aforementioned candidate materials, and the combined thickness of the shielding layers should exceed 100 cm to satisfy the dose limit on the outside surface of the shielding wall of the facility when limiting the thickness of the HDPE-Borax intermediate layer to below 5 cm. However, the shielding wall must include the instrumentation and installation holes for the LSDS system. The radiation leakage through the holes was substantially mitigated by adopting a zigzag-shape with concrete covers on both sides. The suggested optimized design of the shielding structure satisfies the dose rate limit and can be used for the construction of a facility in the near future.

• Radiation Oncology Journal
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• v.9 no.2
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• pp.351-359
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• 1991

The current LINAC technique for radiosurgery utilizes a single isocenter approach with multiple noncoplanar arcs. This approach results in spherical dose distributions in the target. Many arteriovenous malformations and tumors suitable for radiosurgical treatment have non-spherical or irregular shapes. The basic approach presented in this paper is to use two or multiple isocenters with standard arcs to shape irregular target volumes through the use of multiple spherical targets. Selection of reasonable irradiation parameters in the first stage is critical to the success of real-time optimization. A useful guideline for optimum isocenter separation and collimator size is developed to shape the target margin uniformly with an desired isodose surface for an elongated target. The implementation of multiple isocenters with three dimensional dose model and application of multiple isocenters approach to several cases are discussed.

• Korean Journal of Digital Imaging in Medicine
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• v.14 no.2
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• pp.15-22
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• 2012

The purpose of this study was to measure the absorbed dose and calculate the effective dose for cone beam computed tomography (CBCT) and panorama units and to estimate usefulness of x-ray protective. Rando phantom and glass dosimeters were used for dosimetry. The absorbed doses were measured at 15 organs and 14 remainder from correspond to ICRP 2007 recommendations. The absorbed dose was highest in salivary glands as measured CBCT 2.420mGy, panorama 0.307mGy. Absorbed dose in another organs were high in order of thyroid, brain, skin, esophagus. The effective dose was CBCT 0.100mSv, panorama 0.011mSv and effective dose of panorama was higher than that of CBCT by 10 times. In case of wearing x-ray protective, reducing effective dose of CBCT by 0.066mSv (66%) and panorama by 0.008mSv (72%). Effective dose were reduced by radiological shielding but it needs further optimization studies, where dosimetric data are analyzed in combination with image quality with keep the patients' exposure as low as possible.

• Journal of the Korean Society of Radiology
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• v.15 no.4
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• pp.445-453
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• 2021

CT scan is reported to have a high risk of cancer due to a relatively high dose among medical radiological examinations. In particular, exposure to radiation to the breast, which is sensitive to radiation, is inevitable during a chest CT scan for female patient. In this study, the dose reduction effect of wearing a compression band during chest CT scans in women was evaluated, and the lifetime attributable risk due to the effective dose exposed during the CT scan was estimated. As a result, when the compression band was used, the effective tube current decreased as the outer perimeter of the chest became smaller, and it was analyzed that the CT dose index and effective dose were also reduced. In addition, the lifetime attributable risk by chest CT scan was found to reduce the cancer risk by 3.2 per 100,000 for all cancers, 0.2 per 100,000 for solid cancer, and 0.8 per 100,000 for breast cancer, based on women in their 30s when using a compression band. It is judged that the risk of cancer can be reduced through the use of appropriate scan parameters and dose optimization measures such as compression bands for future CT examinations.

• Radiation Oncology Journal
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• v.23 no.3
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• pp.176-185
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• 2005

Purpose: Film dosimetry as a part of patient specific intensity modulated radiation therapy quality assurance (IMRT QA) was peformed to develop a new optimization method of film isocenter offset and to then suggest new quantitative criteria for film dosimetry. Materials and Methods: Film dosimetry was peformed on 14 IMRT patients with head and neck cancers. An optimization method for obtaining the local minimum was developed to adjust for the error in the film isocenter offset, which is the largest part of the systemic errors. Results: The adjust value of the film isocenter offset under optimization was 1 mm in 12 patients, while only two patients showed 2 mm translation. The means of absolute average dose difference before and after optimization were 2.36 and $1.56\%$, respectively, and the mean ratios over a $5\%$ tolerance were 9.67 and $2.88\%$. After optimization, the differences in the dose decreased dramatically. A low dose range cutoff (L-Cutoff) has been suggested for clinical application. New quantitative criteria of a ratio of over a $5\%$, but less than $10\%$ tolerance, and for an absolute average dose difference less than $3\%$ have been suggested for the verification of film dosimetry. Conclusion: The new optimization method was effective in adjusting for the film dosimetry error, and the newly quantitative criteria suggested in this research are believed to be sufficiently accurate and clinically useful.

• Journal of radiological science and technology
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• v.38 no.1
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• pp.1-6
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• 2015

Whole spine scanography (WSS) is a radiological examination that exposes the whole body of the individual being examined to x-ray radiation. WSS is often repeated during the treatment period, which results in a much greater radiation exposure than that in routine x-ray examinations. The aims of the current study were to evaluate the patient dose of WSS using computer simulation, image magnification and angulation of phantom image using different patient position. We evaluated the effective dose(ED) of 23 consecutive patients (M : F = 13:10) who underwent WSS, based on the automatic image pasting method for multiple exposure digital radiography. The Anterior-Posterior position(AP) and Posterior-Anterior position( PA) projection EDs were evaluated based on the PC based Monte Carlo simulation. We measured spine transverse process distance and angulation using DICOM measurement. For all patient, the average ED was 0.069 mSv for AP position and 0.0361 mSv for PA position. AP position calculated double exposure then PA position. For male patient, the average ED was 0.089 mSv(AP) and 0.050 mSv(PA). For female patient, the average ED was 0.0431 mSv(AP) and 0.026 mSv(PA). The transverse process of PA spine image measured 5% higher than AP but angulation of transverse process was no significant differences. In clinical practice, just by change the patient position was conformed to reduce the ED of patient. Therefor we need to redefine of protocol for digital radiography such as WSS. whole spine scanography, effective dose, patient exposure dose, exposure direction. protocol optimization.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.119-125
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• 2006

Purpose: To measure the dose for dose optimization at the reference point (A, B) and the critical organ with multi Purpose brachytherapy phantom (MPBP). For this wort the MPBP was custom made, and designed to reconstruct the treatment applicator using multi function applicator (MFA) in the same way as the treatment of patient. Materials and Methods: Dose measurements were made at the reference points (A, B) and the bladder with thermoluminescence dosimeter (TLD) for four patients with tandem and ovoid of uterine cervix cancer using the phantom. In Phantom, Total 20 times of the measurements were made with 5 times a patient. Results: The results of TLD measurements in MPBP phantom showed the relative error ranging from -3.2% to 3.8% at A point, and -1.4% to 4% at B point and 1.3% to 7.15% at the bladder of reference point. Conclusion: The reproducibility of dose measurement under the same condition as the treatment could be achieved using the custom-made MFA in phantom and the dose at the reference point (A, B) and bladder could be analyzed accurately. The measured dose acquired in MPBP can apply for the dose optimization.

• The Journal of the Korea Contents Association
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• v.14 no.1
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• pp.356-363
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• 2014

Recently pediatric CT has been performed by reduced dose according to tube current modulation이라고, this fact has a possibility more reduce a dose because of strong affect depend on tube current modulation. Almost all MDCT snow show and allow storage of the volume CT dose index (CTDIvol), dose length product (DLP), and effective dose estimations on dose reports, which are essential to assess patient radiation exposure and risks. To decrease these radiation exposure risks, the principles of justification and optimization should be followed. justification means that the examination must be medically indicated and useful. Results is using tube current modulation이라고 tend to the lower kV, the lower effective dose. In case of use a low dose CT protocol, we found a relatively lower effective dose than using tube current modulation. Average effective dose of our studies(brain, chest, abdomen-pelvis) less than 47%, 13.8%, 25.7% of germany reference dose, and 55.7%, 10.2%, 43.6% of UK(United Kingdom) reference dose respectively. when performed examination for reduced dose, we must use tube current modulation and low dose CT protocol including body-weight based tube current adaption.