• Progress in Medical Physics
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• v.30 no.4
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• pp.112-119
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• 2019

Purpose: The advantages of ocular proton therapy are that it spares the optic nerve and delivers the minimal dose to normal surrounding tissues. In this study, it developed a solid eye phantom that enabled us to perform quality assurance (QA) to verify the dose and beam range for passive single scattering proton therapy using a single phantom. For this purpose, a new solid eye phantom with a polymethyl-methacrylate (PMMA) wedge was developed using film dosimetry and an ionization chamber. Methods: The typical beam shape used for eye treatment is approximately 3 cm in diameter and the beam range is below 5 cm. Since proton therapy has a problem with beam range uncertainty due to differences in the stopping power of normal tissue, bone, air, etc, the beam range should be confirmed before treatment. A film can be placed on the slope of the phantom to evaluate the Spread-out Bragg Peak based on the water equivalent thickness value of PMMA on the film. In addition, an ionization chamber (Pin-point, PTW 31014) can be inserted into a hole in the phantom to measure the absolute dose. Results: The eye phantom was used for independent patient-specific QA. The differences in the output and beam range between the measurement and the planned treatment were less than 1.5% and 0.1 cm, respectively. Conclusions: An eye phantom was developed and the performance was successfully validated. The phantom can be employed to verify the output and beam range for ocular proton therapy.

• Journal of Radiation Protection and Research
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• v.41 no.2
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• pp.101-104
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• 2016

Background: To protect the public from natural radioactive materials, the 'Act on safety control of radioactive rays around living environment" was established in Korea. There is an annual effective dose limit of 1 mSv for products, but the activity concentration limit for products is not established yet. Materials and Methods: To suggest the activity concentration limits for consumer goods containing NORM, in this research, we assumed the "small room model" surrounding the ICRP reference phantom to simulate the consumer goods in contact with the human bodies. Using the Monte Carlo code MCNPX, we evaluate the effective dose rate for the ICRP reference phantom in a small room with dimension of phantom size and derived the activity concentration limit for consumer goods. Results and Discussion: The consumer goods have about 1600, 1200 and $19000Bq{\cdot}kg^{-1}$ for $^{226}Ra$, $^{232}Th$ and $^{40}K$, and the activity concentration limits are about six times comparing with the values of building materials. We applied the index to real samples, though we did not consider radioactivity of $^{40}K$, indexes of the some samples are more than 6. However, this index concept using small room model is very conservative, for the consumer goods over than index 6, it is necessary to reevaluate the absorbed dose considering real usage scenario and material characteristics. Conclusion: In this research, we derived activity concentration limits for consumer goods in contact with bodies and the results can be used as preliminary screening tool for consumer goods as index concept.

• Journal of the Korean Society of Radiology
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• v.14 no.3
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• pp.295-301
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• 2020

Radiation exposure exposed during mammography, which is performed for early examination of breast cancer, has also been suggested as a cause of carcinogenesis in the past, and scattered rays generated during examination may cause unnecessary radiation exposure to surrounding organs. In this study, the Monte Carlo simulation was used to evaluate the human organ doses exposed during conventional mammography, and to estimate the dose reduction effect for each organ when using 3D printing materials for radiation protection by scattered rays. As a result of organ dose evaluation, the breast on the opposite side of the examination was about 22.0% of the breast on the test side and about 58.6% on the eye, which was highly influenced by the scattering-ray. When using the 3D printing shield to protect it, the breast on the opposite side of the test showed an effective dose reduction effect at a thickness of 1 mm.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.17
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• pp.7401-7405
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• 2014

Background: Postoperative chemoradiotherapy is accepted as standard treatment for stage IB-IV, M0 gastric cancer. Radiotherapy (RT) planning of gastric cancer is important because of the low radiation tolerance of surrounding critical organs. The purpose of this study was to compare the dosimetric aspects of 2-dimensional (2D) and 3-dimensional (3D) treatment plans, with the twin aims of evaluating the adequacy of 2D planning fields on coverage of planning target volume (PTV) and 3D conformal plans for both covering PTV and reducing the normal tissue doses. Materials and Methods: Thirty-six patients with stage II-IV gastric adenocarcinoma were treated with adjuvant chemoradiotherapy using 3DRT. For each patient, a second 2D treatment plan was generated. The two techniques were compared for target volume coverage and dose to normal tissues using dose volume histogram (DVH) analysis. Results: 3DRT provides more adequate coverage of the target volume. Comparative DVHs for the left kidney and spinal cord demonstrate lower radiation doses with the 3D technique. Conclusions: 3DRT produced better dose distributions and reduced radiation doses to left kidney and spinal cord compared to the 2D technique. For this reason it can be predicted that 3DRT will result in better tumor control and less normal tissue complications.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.17
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• pp.7407-7411
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• 2014

The incidence of urban female breast cancer has been continuously increasing over the past decade with unknown etiology. One hypothesis for this increase is carcinogen exposure from tobacco. Therefore, the objective of this study was to investigate the risk of urban female breast cancer from tobacco smoke exposure. The matched case control study was conducted among Thai females, aged 17-76 years and living in Bangkok or its surrounding areas. A total of 444 pairs of cases and controls were recruited from the Thai National Cancer Institute. Cases were newly diagnosed and histologically confirmed as breast cancer while controls were selected from healthy women who visited a patient, matched by age ${\pm}5$ years. After obtaining informed consent, tobacco smoke exposure data and information on other potential risk factors were collected by interview. The analysis was performed by conditional logistic regression, and presented with odds ratio (ORs) and 95% confidence intervals(CI). From all subjects, 3.8% of cases and 3.4% of controls were active smokers while 11.0% of cases and 6.1% of controls were passive smokers. The highest to lowest sources of passive tobacco smoke were from spouses (40.8%), the workplace (36.8%) and public areas (26.3%), respectively. After adjusting for other potential risk factors or confounders, females with frequent low-dose passive smoke exposure (${\leq}7$ hours per week) from a spouse or workplace had adjusted odds ratio 3.77 (95%CI=1.11-12.82) and 4.02 (95%CI=1.04-15.50) higher risk of breast cancer compared with non-smokers, respectively. However, this study did not find any association of breast cancer risk in high dose passive tobacco smoke exposure, or a dose response relationship in cumulative passive tobacco smoke exposure per week, or in the active smoker group. In conclusion, passive smoke exposure may be one important risk factor of urban female breast cancer, particularly, from a spouse or workplace. This risk factor highlights the importance of avoiding tobacco smoke exposure as a key measure for breast cancer prevention and control.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.4
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• pp.439-446
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• 2023

Objectives: The aims of this study are to investigate how X-rays are emitted to surrounding parts during the ion implantation process, to analyze these emissions in relation to the properties of the ion implanter equipment, and to estimate the resulting exposure dose. Eight ion implanters equipped with high-voltage electrical systems were selected for this study. Methods: We monitored X-ray emissions at three locations outside of the ion implanters: the accelerator equipped with a high-voltage energy generator, the impurity ion source, and the beam line. We used a Personal Portable Dose Rate and Survey Meter to monitor real-time X-ray levels. The SX-2R probe, an X-ray Features probe designed for use with the Radiagem^TM meter, was also utilized to monitor lower ranges of X-ray emissions. The counts per second (CPS) measured by the meter were estimated and then converted to a radiation dose (𝜇Sv/hr) based on a validated calibration graph between CPS and μGy/hr. Results: X-rays from seven ion implanters were consistently detected in high-voltage accelerator gaps, regardless of their proximity. X-rays specifically emanated from three ion implanters situated in the ion box gap and were also found in the beam lines of two ion implanters. The intensity of these X-rays did not show a clear pattern relative to the devices' age and electric properties, and notably, it decreased as the distance from the device increased. Conclusions: In conclusion, every gap, in which three components of the ion implanter devices were divided, was found to be insufficiently shielded against X-ray emissions, even though the exposure levels were not estimated to be higher than the threshold.

• Journal of Veterinary Clinics
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• v.38 no.3
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• pp.135-142
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• 2021

The aim of this study was to evaluate the contrast effect if a saline flush following low-volume contrast medium bolus improves vascular and parenchymal enhancement using a saphenous vein in abdominal CT for small animals. Six clinically healthy beagle dogs underwent abdominal contrast-enhanced CT. They were divided into nine groups (each group, n = 6), according to the volume of contrast medium 1, 2, and 3 mL/kg, and volume of the saline solution 0, 5, and 10 mL. Dynamic CT scanning was performed at the hepatic hilum level. The maximum contrast enhancement, time to maximum enhancement, and time to equilibrium phase were calculated from the time attenuation curves. Mean attenuation values for all groups were measured in the aorta, portal vein, and liver. After contrast enhancement, grading of image quality regarding surrounding artifacts and evaluation of the hepatic hilum structures was performed. For comparison of the effect of the contrast material and saline solution doses, differences in mean attenuation values between the contrast medium 2 mL/kg without saline flush group and the remaining groups, and between contrast medium 3 mL/kg without saline flush group and the remaining groups, were analyzed for statistical significance. There were no significant differences between with and without saline flushing at the same contrast medium dose groups. There were no significant differences in peak values between the 3 mL/kg dose of contrast medium alone and the 2 mL/kg dose of contrast medium with saline solution flush. However, there was a significant difference in peak values between the 3 mL/kg dose of the contrast medium without the saline flush group and the 2 mL/kg dose of the contrast medium alone group. Grades of the artifacts were not significantly different in the saline flush regardless of the dose of the contrast medium. Using 2 mL/kg of contrast medium with saline solution flush resulted in similar liver parenchyma attenuation, compared with using 3 mL/kg of contrast medium without saline solution flush. In CT evaluation of hepatic parenchymal diseases, using 2 mL/kg of contrast medium with saline solution flush may yield decreased risk of contrast nephropathy and cost-saving.

• Journal of the Korean Society of Radiology
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• v.6 no.5
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• pp.343-349
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• 2012

Intensity Modulated Radiotherapy (IMRT) is increasing its use recently due to its benefits of minimizing the dose on surrounding normal organs and being able to target a high dose specifically to the tumor. The study aims to measure and evaluate the dose distribution according to its dynamic changes in Mapcheck. In order to verify the dose distribution by EDW angle($10^{\circ}$,$15^{\circ}$,$20^{\circ}$,$25^{\circ}$,$30^{\circ}$,$45^{\circ}$,$60^{\circ}$), field size (asymmetric field) and depth changes (1.5 cm, 5.0 cm) using IMRT in Clinac ix, a solid phantom was placed on the Mapcheck and 100MU was exposed by 6 MV, 10MV X-ray. Using a 6MV, 10MV energy, the percentage depth dose according to a dynamic changes at a maximum dose depth (1.5 cm) and at 5.0 cm depth showed the value difference of maximum 0.6%, less than 1%, which was calculated by a treatment program device considering the maximum dose depth at the center as 100%, the percentage depth dose was in the range between 2.4% and 7.2%. Also, the maximum value difference of a percentage depth dose was 4.1% in Y2-OUT direction, and 1.7% in Y1-IN direction. When treating a patient using a wedge, it is considered that using an enhanced dynamic wedge is effective to reduce the scattered dose which induces unnecessary dose to the surroundings. In particular, when treating a patient at clinic, a treatment must be performed considering that the wedge dose in a toe direction is higher than the dose in a heel direction.

• 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.

• Progress in Medical Physics
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• v.8 no.1
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• pp.47-52
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• 1997

Simulations were performed using a Monte Carlo technique in order to show physical phenomena occurring when a heavy charged particle such as proton or alpha particle traverses the medium. It was confirmed that the sharp Bragg peak occurred deeper in the water with the increasing proton energy. It is found that the use of such a sharp Bragg peak due to heavy charged particles would be far superior to the case of the photon or electron, since the absorbed dose in the target tissues would be better localized, thereby minimizing the damage to the surrounding tissues.