• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.1001-1007
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• 2023

Dose limits are not applied to medical radiation exposure therefore justification and optimization should be essential for protecting radiation. This study explores methods to reduce exposure dose undergoing general radiation exam by bolus(tissue equivalent material) with keeping image quality. Hand PA projection with 50 kVp, 5 mAs, SID 100 cm, and 8×10 inch is referred by covered bolus of thickness 0, 3, 5, 8, and 10 mm for evaluation entrance dose and SNR. The entrance dose (μGy) to the hand by bolus thickness was 125.41±0.288, 106.85±0.255, 104.97±0.221, 91.68±0.299, and 90.94±0.106 showing a significant reduction in radiation exposure depending on if the bolus was used and bolus thickness. The SNR of the image was 13.997, 13.906, 12.240, 12.538, and 12.548 at each bolus thickness, showing no significant difference. It was confirmed that if appropriate thickness and size of bolus is used depending on the type of radiological imaging exam and the body site, a significant radiation dose reduction effect can be achieved without deteriorating image quality.

• Progress in Medical Physics
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• v.23 no.4
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• pp.269-278
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• 2012

Aquaplast Thermoplastic (AT) is a tissue-equivalent oral compensator that has been developed to improve dose uniformity at the common boundary and around the treated area during radiotherapy in patients with head and neck cancer. In order to assess the usefulness of AT, the degree of improvement in dose distribution and physical properties were compared to those of oral compensators made using paraffin, alginate, and putty, which are materials conventionally used in dental imprinting. To assess the physical properties, strength evaluations (compression and drop evaluations) and natural deformation evaluations (volume change over time) were performed; a Gafchromic EBT2 film and a glass dosimeter inserted into a developed phantom for dose verification were used to measure the common boundary dose and the beam profile to assess the dose delivery. When the natural deformation of the oral compensators was assessed over a two-month period, alginate exhibited a maximum of 80% change in volume from moisture evaporation, while the remaining tissue-equivalent properties, including those of AT, showed a change in volume that was less than 3%. In a free-fall test at a height of 1.5 m (repeated 5 times as a strength evaluation), paraffin was easily damaged by the impact, but AT exhibited no damage from the fall. In compressive strength testing, AT was not destroyed even at 8 times the force needed for paraffin. In dose verification using a glass dosimeter, the results showed that in a single test, the tissue-equivalent (about 80 Hounsfield Units [HU]) AT delivered about 4.9% lower surface dose in terms of delivery of an output coefficient (monitor unit), which was 4% lower than putty and exhibited a value of about 1,000 HU or higher during a dose delivery of the same formulation. In addition, when the incident direction of the beam was used as a reference, the uniformity of the dose, as assessed from the beam profile at the boundary after passing through the oral compensators, was 11.41, 3.98, and 4.30 for air, AT, and putty, respectively. The AT oral compensator had a higher strength and lower probability of material transformation than the oral compensators conventionally used as a tissue-equivalent material, and a uniform dose distribution was successfully formed at the boundary and surrounding area including the mouth. It was also possible to deliver a uniformly formulated dose and reduce the skin dose delivery.

• Journal of radiological science and technology
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• v.32 no.1
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• pp.53-60
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• 2009

This study examined the change in the attenuation of X-rays with the ROI (Region of Interest) in DR (Digital Radiography) according to the stomach contents by manufacturing a tissue equivalent material phantom to simulate real stomach tissue based on the assumption that there is some attenuation of X-rays and a difference in imaging quality according to the stomach contents. The transit dosage by the attenuation of X-rays decreased with increasing protein thickness, which altered the average ROI values in the film and DR images. A comparison of the change in average ROI values of the film and DR image showed that the image in film caused larger density changes with varying thickness of protein than the image by DR. The results indicate that NPO (nothing by mouth) is more important in film system than in DR system.

• Journal of the Korean Society of Radiology
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• v.16 no.6
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• pp.681-686
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• 2022

In this study, a scintillation resin for 3D printing was fabricated with 1.0 wt% of PPO organic scintillator, 5.0 wt% of MMA, and commercial acrylic resin. Using the scintillation resin, 3D-shaped plastic scintillator radiation sensors were successfully fabricated quickly and inexpensively with a commercial 3D DLP printer. The 3D printed plastic scintillator has a good dose-output linearity of R-square 0.998 was obtained in the range of 1 to 10 nA of beam current of the 45 MeV proton beam. The developed 3D plastic scintillator has low light output, so there is a limit to its use in low-dose-rate gamma-ray or X-ray dosimetry. However, it was confirmed that the tissue equivalent material could be usefully used for measuring high energy or high dose rates radiation, such as proton beams and ultra-high dose rate beams.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.75-80
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• 2006

Purpose: In radiation therapy, precise calculation of dose toward malignant tumors or normal tissue would be a critical factor in determining whether the treatment would be successful. The Radiation Treatment Planning (RTP) system is one of most effective methods to make it effective to the correction of dose due to CT number through converting linear attenuation coefficient to density of the inhomogeneous tissue by means of CT based reconstruction. Materials and Methods: In this study, we carried out the measurement of CT number and calculation of mass density by using RTP system and the homemade inhomogeneous tissue Phantom and the values were obtained with reference to water. Moreover, we intended to investigate the effectiveness and accuracy for the correction of inhomogeneous tissue by the CT number through comparing the measured dose (nC) and calculated dose (Percentage Depth Dose, PDD) used CT image during radiation exposure with RTP. Results: The difference in mass density between the calculated tissue equivalent material and the true value was ranged from $0.005g/cm^3\;to\;0.069g/cm^3$. A relative error between PDD of RTP and calculated dose obtained by radiation therapy of machine ranged from -2.8 to +1.06%(effective range within 3%). Conclusion: In conclusion, we confirmed the effectiveness of correction for the inhomogeneous tissues through CT images. These results would be one of good information on the basic outline of Quality Assurance (QA) in RTP system.

• Journal of radiological science and technology
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• v.26 no.2
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• pp.49-56
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• 2003

The purposes of this study are to improve the ultrasound resolution of various nylon and metallic mono-filament wires, therefore, it was tested that it analyze on nylon mono-filament wire of 0.1 mm in A Co.'s ultrasonic phantom and synthesis of C15 g tissue mimicking materials(TMM), analyze resolution of nylon and metallic mono-filament wires in water and TMM. The results obtained were summarized as follows: 1. Metallic mono-filament wire of 0.1 mm and nylon mono-filament wire of 0.12 mm, 180 denier showed that it cleared dot echo pattern. 2. Metallic and nylon mono-filament wire of 0.2 mm showed that it cleared comet tail echo by reverberation artifact. 3. Nylon and metallic mono-filament wire of 0.1 mm showed that it can used for dead zone and axial resolution test. 4. Nylon mono-filament wire compared with metallic mono-filament wire showed that it satisfy elasticity and construction. 5. Degree of hardness of na not changed mono-filament's echo textures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2278-2284
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• 2012

Exposure-dose reducing effect was measured by using bolus, a tissue-equivalent material as a shield to obtain useful diagnostic images while minimizing the radiation exposure of thyroid which is highly sensitive to radiation during panoramic radiography. The experiment was performed within the period of 1 June 2001 through 30 June 2011 by measuring entrance surface dose and deep dose at the thyroid-corresponding site of a head and neck phantom. As a result, the entrance surface dose in the thyroid for using no shield was 43.84 ${\mu}Gy$ on the average, and the thyroid shield of bolus 10 mm in thickness reduced the dose by 15.45 ${\mu}Gy$(35.24%) to 28.39 ${\mu}Gy$ on the average. The use of a 20 mm thyroid shield resulted in the dose of 25.38 ${\mu}Gy$ on the average, a 18.46 ${\mu}Gy$(42.10%) drop from 43.84 ${\mu}Gy$ for using no shield. On the site 20 mm below the surface, a thyroid shield 10 mm in thickness had no dose-reducing effect, while a 20 mm thyroid shield reduced the dose by 0.06 mSv(20%).

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.173-179
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• 2021

Scattered x-ray generated by digital radiography systems also have the advantage of increasing signals, but ultimately detectability is reduced by decreasing resolution and increasing noise of x-ray images transmitted objects. An indirect method of measuring scattered x-ray in a modulation-transfer function (MTF) for evaluating resolution in a spatial-frequency domain can be considered as a drop in the MTF value corresponding to zero-frequency. In this study, polymethyl methacrylate (PMMA) was used as a patient tissue equivalent, and MTFs were obtained for various thicknesses to quantify the effect of scattered x-ray on resolution. X-ray image signals were observed to decrease by 35 ~ 83% with PMMA thickness increasing, which is determined by the absorption or scattering of x-rays in PMMA, resulting in reduced MTF and increased scatter fraction. The method to compensate for MTF degradation by PMMA resulted in the MTF inflation without considering the optical spreading generated by the indirect-conversion type detector. Data fitting or zero-padding are needed to compensate for MTF more reasonably on edge-spread function or line-spread function.

• Progress in Medical Physics
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• v.15 no.1
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• pp.23-29
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• 2004

The relationship between the dose calculated with a radiotherapy treatment planning system (RTPS) and CT number verses the relative electron density curve was investigated for various CT voltages and beam qualifies. We obtained the relationship between the CT numbers and electron densities of the tissue equivalent materials for various CT voltages and beam qualifies. At lower CT voltages, the higher density materials, like cortical bone, showed larger CT numbers and the soft tissues showed no variations. We peformed a phantom study in a RTPS, where a phantom consisted of lung and bone legions in water. We calculated the dose received behind the lung and bone regions for 6 MV photon beams, in which the regions below the lung, water and bone received higher doses in this listed order. The result was the same for 10 MV photon beams. For the clinical application, the doses were calculated for the lung and pelvis. No difference was observed when using different electron density conversion tables with various CT voltages from a same CT. A relative dose difference of 1.5% was obtained when the CT machine for the density conversion table was different from that for the CT image for planning.

• Progress in Medical Physics
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• v.1 no.1
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• pp.31-42
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• 1990

The finding of long lived free radicals produced by ionizing radiation in organic crystals and the quantification of this effect by electron spin resonance(ESR) spactroscopy has proven excellent dosimetric applicability. The tissue equivalent alanine dosimeter also appear appropriate for radiation therapy level dosimetry. The dose measurement was performed in a Rando phantom using high energy photons as produced by high energy medical linear accelerator and cobalt-60 teletherapy unit. The absorbed dose range of the ESR/alanine dosimetry system could be extended down to 0.1 Gy. The response of the alanine dosimeters was determined for photons at different therapeutic dose levels from less than 0.1 Gy to 100 Gy and the depth dose measurements were carried out for photon energies of 1.25MeV, 6 and 10 MV with alanine dosimeters in Rando phantom. Comparisons between ESR/alanine in a Rando phantom and ion chamber in a water phantom were made performing depth dose measurements to examine the agreement of both methods under field conditions.