• Progress in Medical Physics
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• v.8 no.2
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• pp.35-43
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• 1997

The knowledge of x-ray spectra is highly desirable in some investigation involves the differential penetrating power and absorption coefficient correction of various photon beam. The transmission data were obtained from the 80 kVp and 120 kVp of CT x-ray beam with the aluminium filter which is designed in a 30 cm of diameter and pipe-typed filter was prepared from 5.0 mm upto 92.3 mm of thickness. To obtain the reconstructed spectra of CT x-ray, the investigator used the iterative numerical analysis which has been extended to include the tungsten characteristics from experimental transmission data with energy interval of 2 keV. Comparison of the calculated transmission data from the reconstructed spectra with that of measurement shows good agreement in both 80 kVp and 120 kVp x-ray beams. This numerical analysis based on iteratively calculation of fractional exposure per energy interval shows the high potential of usefulness of determination the x-ray spectra from the attenuated beam in diagnostic energy range.

• Journal of the Korean Society of Radiology
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• v.13 no.4
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• pp.667-674
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• 2019

Because examination with technegas produces images through simple diffusion accumulation, the examination room can become contaminated after scan. Therefore, radiation workers and patients awaiting examination will be affected by internal exposure from technegas inhalation. Before and after gravity ventilation, I am trying to find a way to reduce the exposure dose of waiting patients according to a comparative analysis of horizontal spatial dose rates over time. Spatial dose ratio were measured for 10 minutes from various distances and angles around ventilator's location before and after gravity ventilation. Then, mean values, standard deviation and reduction ratio were calculated. The highest reduction rate of gravity ventilation was 95.31% and the highest reduction ratio was 1 to 3 minutes. Therefore, the gravity ventilation could reduce the exposure dose of radiologic technologists, waiting patients, patient guardians and nurses. In conclusion, the reduction of the exposure dose during the technegas ventilation study through gravity ventilation will play a role in optimiging the protection and it is in accordance with the recommended reduction of the medical exposure by ICRP 103.

• 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 the Korea Contents Association
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• v.15 no.11
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• pp.298-306
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• 2015

This study is the material of the additional filter(Cu, Ni, CaWO4, Gd+Ba) being used when the diagnosis X-ray was varied to evaluate the spatial dose distribution accordingly. And it suggest to find a suitable material. Experiments using MCNPX program based on the Monte Carlo simulation method was carried out by selecting the chest and abdomen taken. As a result, each material per dose, the average scatter dose is approximately 62%, 100 cm radius of the point of the simulated body surface exposure dose and 50 cm radius centered on the point average about 47%. It is determined that an Al material is currently available in accordance with the result to be replaced by Cu, Ni material is sufficient. With just the thickness due to the difference in the atomic number and density adjusted to be about one-tenth of the Al it will be suitable.

• Progress in Medical Physics
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• v.9 no.3
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• pp.185-192
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• 1998

It is necessarily to evaluate the energy of X-ray emitted from linear accelerator in order to determine the accurate absorbed dose. The method of direct measurement for x-ray energy is very difficult and impractical. Therefore the method of using beam quality index is generally used. Several dosimetry protocols recommend the use of quality indices such as depth of dose maximum at radiation central axis, dose gradient, and dose level. The linear accelerator manufactures follow the recommendation as dosimetry protocols. The study was performed for us to select the most suitable parameter among the Quality indices as described above. For photon beams of 4, 6, 10, 15, and 21 MV nominal energies produced by four kinds of accelerators(Mitsubishi, Scanditronix, Siemens, Varian) in eleven institutions, We evaluated the x-ray energies obtained by the Quality indices as recommended by several dosimetry protocols and manufactures. Results showed that there were energy spreads according to the same accelerators and Quality indices even though nominal energies were same. It appeared that the percent depth dose at 10 cm (D$_{10}$(%)) gave the smallest deviation and spread of energies. As energies increased, the energy deviation increased for all the quality indices. It is desirable for the use of unified quality index to compare the evaluation of beam quality at different institutions.

• Progress in Medical Physics
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• v.15 no.2
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• pp.105-111
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• 2004

The parallel plate detector with dielectric film for dosimetry was designed to measure detection characteristic of 6 MV X-ray with medical linear accelerator. PTFE film was inserted into FEP films that are made by two one-side metal coated materials for ion source. The thicknesses of PTFE dielectric film was 100 ${\mu}{\textrm}{m}$ and the thickness of FEP dielectric film was 100 ${\mu}{\textrm}{m}$, respectively. This detector was fixed by two acrylic plate for physical hardness ad geometrical consistency. The geometrical condition for measurement with parallel-plate for detector was below; SSD=100 cm and the 5 cm depth between detector and phantom surface The major parameter of detector characteristics such as zero drift current, leakage current, charge response by applied voltage, reproducibility, linearity, TMR measurement, dose rate effect were measured. The zero drift currents are 8.3 pA and leakage currents are 10 pA. The charge response of applied voltage is showing linearity in 414 voltage. The measurement deviation of reproducibility in this detector is within 1% for dose and the linearity of applied dose shows in this detector. The TMR curves in phantom between this parallel plate detector and reference detector are matched within 3% deviation from maximum dose depth to 7.5 cm depth. It is considered that this dosimetric system is satisfactory for the purpose of the constancy check of the 6 MV x-ray from medical linear accelerator.

• Progress in Medical Physics
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• v.16 no.3
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• pp.125-129
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• 2005

The first step in the commissioning procedure of a treatment planning system is always verification of the basic beam data. In this work, we have measured POD curves and beam profiles between 1 $\times$ 1 cm$^{2}$ and 40 $\times$ 40 cm$^{2}$ . In an attempt, Pinnacle 7.4f detect discrepancies between predicted dose distribution and delivered dose distribution. The discrepancies between measurement data and caculation data was found. The delivered dose was underestimated in field but overestimated out of field. The D$_{max}$ depth of 1 $\times$ 1 cm$^{2}$ was reduced about 2 mm. For the larger field size ($\geq$4$\times$4 cm$^{2}$, the beam profile and PDD curve showed good agreement between measurement data and calculation data.

• Progress in Medical Physics
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• v.23 no.4
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• pp.317-325
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• 2012

The Varian PORTALVISION (Varian Medical Systems, US) shows significant overresponses as the off-center distance increases compared to the predicted dose. In order to correct the dose discrepancy, the off-axis correction is applied to VARIAN iX linear accelerators. The portal dose for $38{\times}28cm^2$ open field is acquired for 6 MV, 15 MV photon beams and also are predicted by PDIP algorithm under the same condition of the portal dose acquisition. The off-axis correction is applied by modifying the $40{\times}40cm^2$ diagonal beam profile data which is used for the beam profile calibration. The ratios between predicted dose and measured dose is modeled as a function of off-axis distance with the $4^{th}$ polynomial and is applied to the $40{\times}40cm^2$ diagonal beam profile data as the weight to correct measured dose by EPID detector. The discrepancy between measured dose and predicted dose is reduced from $4.17{\pm}2.76$ CU to $0.18{\pm}0.8$ CU for 6 MV photon beam and from $3.23{\pm}2.59$ CU to $0.04{\pm}0.85$ CU for 15 MV photon beam. The passing rate of gamma analysis for the pyramid fluence patten with the 4%, 4 mm criteria is improved from 98.7% to 99.1% for 6 MV photon beam, from 99.8% to 99.9% for 15 MV photon beam. IMRT QA is also performed for randomly selected Head and Neck and Prostate IMRT plans after applying the off-axis correction. The gamma passing rare is improved by 3% on average, for Head and Neck cases: $94.7{\pm}3.2%$ to $98.2{\pm}1.4%$, for Prostate cases: $95.5{\pm}2.6%$, $98.4{\pm}1.8%$. The gamma analysis criteria is 3%, 3 mm with 10% threshold. It is considered that the off-axis correction might be an effective and easily adaptable means for correcting the discrepancy between measured dose and predicted dose for IMRT QA using EPID in clinic.

• Proceedings of the Korean Society of Radiological Science
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• 1999.10a
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• pp.75.1-75.1
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• 1999

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.107-114
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• 2012

Purpose: Unlike the existing linear accelerator with photon, proton therapy produces a number of second radiation due to the kinds of nuclide including neutron that is produced from the interaction with matter, and more attention must be paid on the exposure level of radiation workers for this reason. Therefore, thermoluminescence dosimeter (TLD) that is being widely used to measure radiation was utilized to analyze the exposure level of the radiation workers and propose a basic data about the radiation exposure level during the proton therapy. Materials and Methods: The subjects were radiation workers who worked at the proton therapy center of National Cancer Center and TLD Badge was used to compare the measured data of exposure level. In order to check the dispersion of exposure dose on body parts from the second radiation coming out surrounding the beam line of proton, TLD (width and length: 3 mm each) was attached to on the body spots (lateral canthi, neck, nipples, umbilicus, back, wrists) and retained them for 8 working hours, and the average data was obtained after measuring them for 80 hours. Moreover, in order to look into the dispersion of spatial exposure in the treatment room, TLD was attached on the snout, PPS (Patient Positioning System), Pendant, block closet, DIPS (Digital Image Positioning System), Console, doors and measured its exposure dose level during the working hours per day. Results: As a result of measuring exposure level of TLD Badge of radiation workers, quarterly average was 0.174 mSv, yearly average was 0.543 mSv, and after measuring the exposure level of body spots, it showed that the highest exposed body spot was neck and the lowest exposed body spot was back (the middle point of a line connecting both scapula superior angles). Investigation into the spatial exposure according to the workers' movement revealed that the exposure level was highest near the snout and as the distance becomes distant, it went lower. Conclusion: Even a small amount of exposure will eventually increase cumulative dose and exposure dose on a specific body part can bring health risks if one works in a same location for a long period. Therefore, radiation workers must thoroughly manage exposure dose and try their best to minimize it according to ALARA (As Low As Reasonably Achievable) as the International Commission on Radiological Protection (ICRP) recommends.