• Journal of radiological science and technology
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• v.46 no.2
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• pp.89-97
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• 2023

With the introduction of the D.R system, the grid with high removal rate of scattered radiation is selected and used without considering the grid performance evaluation. Despite the high removal rate of scattered radiation belonging to high grid ratio, it is also possible to see the cut-off phenomenon in which the primary ray involved in the formation of image could be removed as well. Thus, the purpose of this study is to provide the basic data for researches on the usefulness of using the grid by presenting the appropriate grid ratio in the D.R system through the measurement of image in grid such as non-grid, 6:1, 8:1, 10:1, 12:1. The equipments used for this study were radiation generator with grid in 12:1, 10:1, 8:1, 6:1, indirect-type detector, and acryl phantom. As the study for image evaluation, this study measured the SNR, PSNR, MSE, and Entropy. In the results of this study, the PSNR was the highest in 6:1 and the lowest in 8:1. The SNR was high in 6:1 and 8:1, and the lowest in 12:1. In case of Entropy, it was high in 8:1 and 10:1, and the lowest in 12:1. Therefore, when the grid is used, it would be more proper to choose the grid in 8:1 or 10:1 with less loss in information content of primary ray rather than the high grid ratio showing the increased patient exposure dose.

• Journal of the Korean Society of Radiology
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• v.12 no.3
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• pp.313-319
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• 2018

In radiation treatment, it is unavoidable to block the influence of scattered ray on a skin and prevent internal normal organs from being exposed to radiation. It is fair to say that radiation therapy aims to reduce an absorbed dose of normal tissues. In particular, in radiation therapy of left-sided breast cancer, the internal neighboring organs are normal breast tissues, the heart, and the lung. The side effects on the heart include cardioplegy and myocardial infarction. This study tried to observe changes in the volume and dose of the heart in general radiation therapy plan and respiratory control based radiation therapy plan for patients with left-sided breast cancer, and to find the heart's volume and dose generated by respiration. According to the 4D computer tomography (CT), a volume of the heart had $12.8{\pm}8.7cc$ on average, and its dose had $17.3{\pm}12.1cGy$ on average. The differences in the volume and dose may cause side effects in radiation treatment. Therefore, it is necessary to apply respiratory control technique to establish the radiation treatment plan based on an accurate position of the heart.

• Radiation Oncology Journal
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• v.7 no.1
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• pp.133-140
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• 1989

Three-dimension paraffin compensator was designed to construct the tissue equivalent compensator for irregular body contours and obiliques beam incidence. The ratio of compensator thickness to tissue deficit was depended on field size, depth and air gap because the scattered dose loss. The ratio of compensator-tissue was optimized 0.79, 0.73, 0.61 and 0.56 in 6MV x-rays as function of field size $4{\times}4$, $10{\times}10$, $20{\times}20$ and $30{\times}30cm^2$ respectively. in our study. Using this tissue equivalent compensator, it can be got 2% difference of dose at same mid-plane in phantom study.

• Journal of Radiation Protection and Research
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• v.36 no.1
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• pp.23-27
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• 2011

In order to confirm feasibility of MOSFET modality in use of in.vivo dosimetry, evaluation of gonad shielding in order to minimize gonadal dose of patients undergoing radiotherapy by using MOSFET modality was performed. Gonadal dose of patients undergoing radiotherapy for rectal cancer in the department of radiation oncology of Seoul National University Hospital since 2009 was measured. 6 MV and 15 MV photon beams emitted from Varian 21EX LINAC were used for radiotherapy. In order to minimize exposed dose caused by the scattered ray not only from collimator of LINAC but also from treatment region inside radiation field, we used box.shaped lead shielding material. The shielding material was made of the lead block and consists of $7.5\; cm\;{\times}\;9.5\;cm\;{\times}5.5\;cm$ sized case and $9\;cm\;{\times}\;9.5\;cm\;{\times}\;1\;cm$ sized cover. Dosimetry for evaluation of gonad shielding was done with MOSFET modality. By protecting with gonad shielding material, average gonadal dose of patients was decreased by 23.07% compared with reference dose outside of the shielding material. Average delivered gonadal dose inside the shielding material was 0.01 Gy. By the result of MOSFET dosimetry, we verified that gonadal dose was decreased by using gonad shielding material. In compare with TLD dosimetry, we could measure the exposed dose easily and precisely with MOSFET modality.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.327-335
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• 2003

The commercially available neutron survey meter, the REM500, which uses a tissue equivalent proportional counter (TEPC) and the self-constructed TEPC were used to determine the microdosimetric quantities of several neutron calibration fields at Korea Atomic Energy Research Institute (KAERI). Microdosimetric spectra, absorbed dose, dose equivalent as well as quality factor were derived and compared with several neutron fields which were produced by using the shadow objects to make neutron scattered and being used as a kind of realistic neutron calibration fields at KAERI. The response of REM500 as a function of mean energy was evaluated with these neutron fields using the counts measured and the predetermined reference value. The response of the self-made TEPC and the REM500 was compared using one of the neutron calibration filelds of a $^{252}Cf$ source. The reference quantities of scattered neutron calibration fields were determined using a Bonner Sphere (BS). The value of frequency-mean lineal energy, dose-mean lineal energy and quality factor of two $^{252}Cf$ sources (unmoderated and $D_2O$ moderated) were determined to check the differences in the reference neutron fields between KAERI and Pacific Northwest National Laboratory (PNNL, USA) and the results were in good agreement within 1%. It means that there is no big difference in dosimetric quantifies of neutron calibration fields of two laboratories.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.265-272
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• 2014

Purpose : To reduce the radiation dose to the thyroid that is affected to scattered radiation, the shield was used. And we evaluated the shielding effect for the thyroid during whole brain radiation therapy. Materials and Methods : To measure the dose of the thyroid, 300cGy were delivered to the phantom using a linear accelerator(Clinac iX VARIAN, USA.)in the way of the 6MV X-ray in bilateral. To measure the entrance surface dose of the thyroid, five glass dosimeters were placed in the 10th slice's surface of the phantom with a 1.5 cm interval. The average values were calculated by measured values in five times each, using bismuth shield, 0.5 mmPb shield, self-made 1.0 mmPb shield and unshield. In the same location, to measure the depth dose of the thyroid, five glass dosimeters were placed in the 10th slice by 2.5 cm depth of the phantom with a 1.5 cm interval. The average values were calculated by measured values in five times each, using bismuth shield, 0.5 mmPb shield, self-made 1.0 mmPb shield and unshield. Results : Entrance surface dose of the thyroid were respectively 44.89 mGy at the unshield, 36.03 mGy at the bismuth shield, 31.03 mGy at the 0.5 mmPb shield and 23.21 mGy at a self-made 1.0 mmPb shield. In addition, the depth dose of the thyroid were respectively 36.10 mGy at the unshield, 34.52 mGy at the bismuth shield, 32.28 mGy at the 0.5 mmPb shield and 25.50 mGy at a self-made 1.0 mmPb shield. Conclusion : The thyroid was affected by the secondary scattering dose and leakage dose outside of the radiation field during whole brain radiation therapy. When using a shield in the thyroid, the depth dose of thyroid showed 11~30% reduction effect and the surface dose of thyroid showed 20~48% reduction effect. Therefore, by using the thyroid shield, it is considered to effectively protect the thyroid and can perform the treatment.

• Journal of the Korean Society of Radiology
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• v.5 no.3
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• pp.155-159
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• 2011

The purposed of this study were measured the radiation exposure of patients and workers by generators, and the protection state for radiation facilities. The subject of the study by X-ray generators in university hospitals of capital area, we measured the maximum irradiation condition of 80 kVp, 200 mA, 0.1 second in the control entrance, control room window, entrance of radiography, adjacent site. The leakage dose per week was which the control entrance was 0.11 mR/week, control room window was 0.15 mR/week, entrance of radiography was 0.12 mR/week and adjacent site was 0.06 mR/week with X-ray unit the mean And the leakage mean dose was 0.11 mR/week. Diagnostic X-ray tubes must ensure that the leakage radiation in the maximum leakage dose in week emitted by the tube outside the useful beam does not exceed certain levels provided by standards.

• Journal of radiological science and technology
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• v.32 no.4
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• pp.393-399
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• 2009

In this study, we measured the dose distribution of scattered ray in X-ray radiography room using an ion chamber and examined the dependency of scattered ray content on the scattered ray source and exposure condition. To study the factors of scattered ray occurrence in the acryl phantom, we measured the change in the scatted ray content according to the X-ray tube voltage (40~140 kV) and the field size ($10{\times}10\;cm^2$, $20{\times}20\;cm^2$, $35{\times}35\;cm^2$). For the $35{\times}35\;cm^2$ field size, the side-scattering rate ranged from 3.1% to 14.5%. The scattered ray contributions of the phantom, collimator, X-ray tube and wall were also measured. The scattered ray contribution of the phantom was higher than 95.4% for the entire tube voltage, and those of the collimator, X-ray tube and wall were 2.6%, 1.3% and 0.7%, respectively.

• The Journal of Korean Society for Radiation Therapy
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• v.19 no.2
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• pp.77-82
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• 2007

Purpose: This study investigates peripheral dose from physical wedge and dynamic wedge system on a multileaf collimator (MLC) equipment linear accelerator. Materials and Methods: Measurments were performed using a 2D array ion chamber and solid water phantom for a 10$\times$10 cm, source-surface distance (SSD) 90 cm, 6 and 15 MV photon beam at depths of 0.5 cm, 5 cm through dmax. Measurments of peripheral dose at 0.5 cm and 5 cm depths were performed from 1 cm to 5 cm outside of fields for the dynamic wedge and physical wedge 15$^\circ$, 45$^\circ$. Dose profiles normalized to dose at the maximum depth. Results: At 6 MV photon beam, the average peripheral dose of dynamic wedge were lower by 1.4% and 0.1%. At 15 MV photon beam, the peripheral dose of dynamic wedge were lower by maximum 1.6%. Conclusion: This study showed that dynamic wedge can reduce scattered dose of clinical organ close to the field edge and reduced treatment time. The wedge systems produce significantly different peripheral dose that should be considered in properly choosing a wedge system for clinical use.

• Journal of the Korean Society of Radiology
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• v.10 no.6
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• pp.381-385
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• 2016

This study aims to propose a method for reducing radiation dose in high-voltage radiography using air gap technique while maintaining the same image quality as when using grids. For an experiment, air gaps were set at 10 cm, 15 cm, 20 cm, 25 cm, and 30 cm with a focus-receptor distance of 180 cm; with each air gap distance, tube current was set at 15 mAs, and tube voltage was set at 80 kVp, 85 kVp, 90 kVp, 95 kVp and 100 kVp. Then, radiographs were taken. In a situation of employing a conventional method of using grids, radiographs were taken at 15 mAs and 107 kVp with a focus-receptor distance of 180 cm. According to the results of the experiment, the surface radiation dose from radiography using grids was 0.130 R; the surface radiation dose at a 20cm air gap was 0.124 R; PSNR between these two images was 10.65 [dB]. In conclusion, the air gap distance, which could maintain the image quality similar to that of a case where scattered radiation was removed and grids were used with a small surface radiation dose, was 20 cm. The result of this study is thought to be used as an indicator to remove surface radiation dose in radiography using air gap.