• Tuberculosis and Respiratory Diseases
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• v.57 no.2
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• pp.118-124
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• 2004

Lung cancer is the leading cause of cancer death for men and women in the industrialized world. It is desirable to detect disease at a stage when it is not causing symptoms and when control or cure is possible. If the screening test detects patients with the disease at an early stage, they can be examined to confirm the diagnosis and intervention can alter the natural history of the disease. The results of screening programs designed to detect early lung cancer using either conventional chest radiograph or sputum cytology are disappointing for a diagnostic screening test. Because of advances in helical CT imaging techniques, screening for lung cancer has been suggested as a possible method of improving outcome. Findings in recent publications suggest that substantial dose reduction is possible in chest CT. The advantages of low-dose CT are more sensitive than chest radiograph for detecting small pulmonary nodules that may be lung cancers, shorter scanning time than conventional chest CT scan without intravenous contrast injection, cheaper cost than standard CT, low radiation dose. However, the true clinical significance of the small tumors found by screening is still unknown, and their effect on mortality awaits future investigation. Furthermore, in addition to detecting an increased number of lung cancers, low-dose CT found at least one indeterminate nodule in many of all screened patients. The majority should be benign but evaluation of all these indeterminate nodules is not a trivial problem in routine practice. In conclusion, lung cancer screening with low-dose CT is a complex subject. The true effectiveness of lung cancer screening (a reduction in mortality from lung cancer) with low-dose CT can be determined through well-designed randomized control trials with enrolment of appropriate subjects.

• Journal of the Korean Society of Radiology
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• v.7 no.2
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• pp.145-149
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• 2013

Helical Tomotherapy is an innovative means of delivering intensity modulated radiation therapy (IMRT) using a device that merges features of a linear accelerator and helical computed tomography (CT) scanner. Hereat, during helical tomotherapy process, megavoltage computed tomography (MVCT) image are usually used for guiding the precise set-up of patient before/after treatment delivery. But which would certainly increase the total dose for patients, this study was to investigate the imaging dose of MVCT using the cylindrical "Cheese" phantom on a tomotherapy machine. A set of cylindrical "Cheese" phantom was adopted for scanning with respectively pitch value (1, 2, 3 mm) with same number slice (10 slice), same length (approximately 9 cm) and phantom set-ups on the couch of tomotherapy system. The average MVCT imaging dose were measured using A1SL ion chamber inserted in the phantom with preset geometry. The MVCT scanning average dose for the cylindrical "Cheese" phantom was 2.24 cGy, 1.02 cGy, 0.81 cGy during respectively pitch value (pitch 1, 2, 3 mm) with same number slice (10 slice), and same length's average dose was 2.47 cGy, 1.28 cGy, 0.88 cGy respectively (pitch 1, 2, 3 mm). Two major parameters, the assigned pitch numbers and scanning length, where the most important impacts to the dose variation. The MVCT dose was inversely proportional to the CT pitch value. The results may provide a reliable guidance for proper planning design of the scanning region, which is valuable to help minimize the extra dose to patient. Questionnaires were distributed to Radiology departments at hospitals with 300 sickbeds throughout the Pohang region of North Gyeongsang Province concerning awareness and performance levels of infection control. The investigation included measurements of the pollution levels of imaging equipment and assistive apparatuses in order to prepare a plan for the activation of prevention and management of hospital infections. The survey was designed to question respondents in regards to personal data, infection management prevention education, and infection management guidelines.

• Journal of the Korean Society of Radiology
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• v.13 no.3
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• pp.473-479
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• 2019

PET-CT improves performance and reduces the time by combining PET and CT of spatial resolution, and uses CT scan for attenuation correction. This study analyzed PET image evaluation. The condition of the tube voltage and current of CT will be changed using. Uniformity phantom and resolution phantom were injected with 37 MBq $^{18}F$ (fluorine ; 511 keV, half life - 109.7 min), respectively. PET-CT (Biograph, siemens, US) was used to perform emission scan (30 min) and penetration scan. And then the collected image data were reconstructed in OSEM-3D. The same ROI was set on the image data with a analyzer (Vinci 2.54, Germany) and profile was used to analyze and compare spatial resolution and image quality through FWHM and SI. Analyzing profile with pre-defined ROI in each phantom, PET image was not influenced by the change of tube voltage or exposure dose. However, CT image was influenced by tube voltage, but not by exposure dose. When tube voltage was fixed and exposure dose changed, exposure dose changed too, increasing dose value. When exposure dose was fixed at 150 mA and tube voltage was varied, the result was 10.56, 24.6 and 35.61 mGy in each variables (in resolution phantom). In this study, attenuation image showed no significant difference when exposure dose was changed. However, when exposure dose increased, the amount of dose that patient absorbed increased too, which indicates that CT exposure dose should be decreased to minimum to lower the exposure dose that patient absorbs. Therefore future study needs to discuss the conditions that could minimize exposure dose that gets absorbed by patient during PET-CT scan.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.109-115
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• 2021

This study is a study on the difference in dose according to the presence or absence of gonadal shielding of scattered rays generated during chest computed tomography examination, and the scattered dose of the examination site was measured by placing the RadEye G-10 device in the center of the phantom. When the gonads are not shielded, the scattering lines of the whole, both sides, posterior and gonads are measured and Xenolite nolead Apron (0.35 mm PB), Xenolite nolead Apron (front 0.35 mm PB Mix back 0.25 mm PB, Skirt overlap), Half Apron After shielding with (0.5 mm PB), each scattered dose was measured. During chest computed tomography, the scattered dose of the test site was measured at 272 μSv, and when not shielded with Apron, the average total was 43 μSv, left 81 μSv, right part 82 μSv, posterior part 38.8 μSv, and Gonad part 16 μSv. Became. Xenolite nolead Apron shielded only the upper part and measured all 11.2 μSv, left part 43.1 μSv, right part 45.3 μSv, posterior part 12 μSv and Gonad part 5.2 μSv. Xenolite nolead Apron (Skirt overlap) covered the Pelvis area 360° and the dose was measured to be 5.6 μSv in the whole, 22.4 μSv in the left, 15.7 μSv in the right side, 6 μSv in the posterior part, and 3.2 μSv in the Gonad part. Xenolite nolead Apron (Skirt overlap) covered the Pelvis area 360° and the dose was measured to be 5.6 μSv in the whole, 22.4 μSv in the left, 15.7 μSv in the right side, 6 μSv in the posterior part, and 3.2 μSv in the Gonad part. When measuring only the upper part with Half Apron, the total measurement was 10.7 μSv, the left part 42.6 μSv, the right part 40.6 μSv, the posterior part 11.3 μSv, and the Gonad part 4.7 μSv. The method of 360° shielding of the pelvic area showed a dose reduction of more than 80%, and a dose reduction effect of more than 70% was shown when all shielding was performed. In all computerized tomography examinations, research to reduce the exposure dose and various shielding devices were used. It is believed that continuous research on the technique is needed.

• Progress in Medical Physics
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• v.25 no.1
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• pp.37-45
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• 2014

The accuracy and uniformity of CT numbers are the main causes of radiation dose calculation error. Especially, for the dose calculation based on kV-Cone Beam Computed Tomography (CBCT) image, the scatter affecting the CT number is known to be quite different by the object sizes, densities, exposure conditions, and so on. In this study, the scatter impact on the CBCT based dose calculation was evaluated to provide the optimal condition minimizing the error. The CBCT images was acquired under three scatter conditions ("Under-scatter", "Over-scatter", and "Full-scatter") by adjusting amount of scatter materials around a electron density phantom (CIRS062, Tissue Simulation Technology, Norfolk, VA, USA). The CT number uniformities of CBCT images for water-equivalent materials of the phantom were assessed, and the location dependency, either "inner" or "outer" parts of the phantom, was also evaluated. The electron density correction curves were derived from CBCT images of the electron density phantom in each scatter condition. The electron density correction curves were applied to calculate the CBCT based doses, which were compared with the dose based on Fan Beam Computed Tomography (FBCT). Also, 5 prostate IMRT cases were enrolled to assess the accuracy of dose based on CBCT images using gamma index analysis and relative dose differences. As the CT number histogram of phantom CBCT images for water equivalent materials was fitted with a gaussian function, the FHWM (146 HU) for "Full-scatter" condition was the smallest among the FHWM for the three conditions (685 HU for "under scatter" and 264 HU for "over scatter"). Also, the variance of CT numbers was the smallest for the same ingredients located in the center and periphery of the phantom in the "Full-scatter" condition. The dose distributions calculated with FBCT and CBCT images compared in a gamma index evaluation of 1%/3 mm criteria and in the dose difference. With the electron density correction acquired in the same scatter condition, the CBCT based dose calculations tended to be the most accurate. In 5 prostate cases in which the mean equivalent diameter was 27.2 cm, the averaged gamma pass rate was 98% and the dose difference confirmed to be less than 2% (average 0.2%, ranged from -1.3% to 1.6%) with the electron density correction of the "Full-scatter" condition. The accuracy of CBCT based dose calculation could be confirmed that closely related to the CT number uniformity and to the similarity of the scatter conditions for the electron density correction curve and CBCT image. In pelvic cases, the most accurate dose calculation was achievable in the application of the electron density curves of the "Full-scatter" condition.

• Journal of Biomedical Engineering Research
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• v.39 no.3
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• pp.116-123
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• 2018

This study is a model experimental study using a phantom to propose an optimized brain CT scan protocol that can reduce the radiation dose of a patient and remain quality of image. We investigate the CT scan parameters of brain CT in clinical medical institutions and to measure the important parameters that determine the quality of CT images. We used 52 multislice spiral CT (SOMATOM Definition AS+, Siemens Healthcare, Germany). The scan parameters were tube voltage (kVp), tube current (mAs), scan time, slice thickness, pitch, and scan field of view (SFOV) directly related to the patient's exposure dose. The CT dose indicators were CTDIvol and DLP. The CT images were obtained while increasing the imaging conditions constantly from the phantom limit value (Q1) to the maximum value (Q4) for AAPM CT performance evaluation. And statistics analyzed with Pearson's correlation coefficients. The result of tube voltage that the increase in tube voltage proportionally increases the variation range of the CT number. And similar results were obtained in the qualitative evaluation of the CT image compared to the tube voltage of 120 kVp, which was applied clinically at 100 kVp. Also, the scan conditions were appropriate in the tube current range of 250 mAs to 350 mAs when the tube voltage was 100 kVp. Therefore, by applying the proposed brain CT scanning parameters can be reduced the radiation dose of the patient while maintaining quality of image.

• Radiation Oncology Journal
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• v.31 no.1
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• pp.12-17
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• 2013

Purpose: Parotid gland can be considered as a risk organ in whole brain radiotherapy (WBRT). The purpose of this study is to evaluate the parotid gland sparing effect of computed tomography (CT)-based WBRT compared to 2-dimensional plan with conventional field margin. Materials and Methods: From January 2008 to April 2011, 53 patients underwent WBRT using CT-based simulation. Bilateral two-field arrangement was used and the prescribed dose was 30 Gy in 10 fractions. We compared the parotid dose between 2 radiotherapy plans using different lower field margins: conventional field to the lower level of the atlas (CF) and modified field fitted to the brain tissue (MF). Results: Averages of mean parotid dose of the 2 protocols with CF and MF were 17.4 Gy and 8.7 Gy, respectively (p < 0.001). Mean parotid dose of both glands ${\geq}20$ Gy were observed in 15 (28.3%) for CF and in 0 (0.0%) for MF. The whole brain percentage volumes receiving >98% of prescribed dose were 99.7% for CF and 99.5% for MF. Conclusion: Compared to WBRT with CF, CT-based lower field margin modification is a simple and effective technique for sparing the parotid gland, while providing similar dose coverage of the whole brain.

• Journal of Radiation Protection and Research
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• v.40 no.1
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• pp.17-24
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• 2015

To improve accuracy of dose calculation on kilovoltage cone beam computed tomography (kV CBCT) images, a custom-made phantom was fabricated to acquire an accurate CT number to electron density curve by full scatter of cone beam x-ray. To evaluate the dosimetric accuracy, 9 volumetric modulated arc therapy (VMAT) plans for head and neck (HN) cancer and 9 VMAT plans for lung cancer were generated with an anthropomorphic phantom. Both CT and CBCT images of the anthropomorphic phantom were acquired and dose-volumetric parameters on the CT images with CT density curve (CTCT), CBCT images with CT density curve ($CBCT_{CT}$) and CBCT images with CBCT density curve ($CBCT_{CBCT}$) were calculated for each VMAT plan. The differences between $CT_{CT}$ vs. $CBCT_{CT}$ were similar to those between $CT_{CT}$ vs. $CBCT_{CBCT}$ for HN VMAT plans. However, the differences between $CT_{CT}$ vs. $CBCT_{CT}$ were larger than those between $CT_{CT}$ vs. $CBCT_{CBCT}$ for lung VMAT plans. Especially, the differences in $D_{98%}$ and $D_{95%}$ of lung target volume were statistically significant (4.7% vs. 0.8% with p = 0.033 for $D_{98%}$ and 4.8% vs. 0.5% with p = 0.030 for $D_{95%}$). In order to calculate dose distributions accurately on the CBCT images, CBCT density curve generated with full scatter condition should be used especially for dose calculations in the region of large inhomogeneity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4411-4417
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• 2010

This study was retrospectively to compare the exposure dose and the imaging quality in coronary CT angiography by using the 64 channel multidetector computed tomography and the 128 channel DSCT. Effective dose was calculated dose length product (DLP) by multiplied the convention factor of chest (0.017). Imaging quality was assessed by radiologists using the 5-point Likert scale. The DLP was ranged from 851 to $1277mGy{\cdot}cm$ (mean: 17.23 mSv) in the 64 channel MDCT and from 82 to $110mGy{\cdot}cm$ (mean: 1.58 mSv) in the of 128 channel DSCT, respectively. The score of imaging quality was respectively $3.31{\pm}0.62$ in 64 channel MDCT and $4.05{\pm}0.46$ in the 128 channel DSCT. The exposure dose of 128 channel DSCT has decreased 1ess 1/10. The score of imaging quality was significant difference between two modalities and the frequency (>4 good) in the 128 channel DSCT is about three times than that of the 64 channel MDCT. Therefore, the 128 channel DSCT in coronary CT angiography is clinically more effective modality for both investigators and patients.

• Imaging Science in Dentistry
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• v.38 no.1
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• pp.7-15
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• 2008

Purpose: This study provides comparative measurements of absorbed and effective doses for newly developed cone beam computed tomography (CT) in comparison with these doses for conventional CT. Materials and Methods: Thermoluminescent dosimeter rods (TLD rod: GR-200, Thermo Fisher Scientific Inc., Waltham, MA, USA) were placed at 25 sites throughout the layers of Male ART Head and Neck Phantom (Radiology Support Devices Inc., Long Beach, USA) for dosimetry. Implagraphy, DCT Pro (Vatech Co., Hwasung, Korea) units, SCT-6800TXL (Shimadzu Corp., Kyoto, Japan), and Crane x 3+(Soredex Orion Corp., Helsinki, Finland) were used for radiation exposures. Absorption doses were measured with Harshaw 3500TLD reader (Thermo Fisher Scientific Inc., Waltham, MA, USA). Radiation weighted doses and effective doses were measured and calculated by 2005 ICRP tissue weighting factors. Results: Absorbed doses in Rt. submandibular gland were 110.57 mGy for SCT 6800TXL (Implant), 24.56 mGy for SCT 6800TXL (3D), 22.39 mGy for Implagraphy 3, 7.19 mGy for DCT Pro, 5.96 mGy for Implagraphy 1, 0.70 mGy for Cranex 3+. Effective doses $(E_{2005draft)$ were 2.551 mSv for SCT 6800TXL (Implant), 1.272 mSv for SCT 6800TXL (3D), 0.598 mSv for Implagraphy 3, 0.428 mSv for DCT Pro and 0.146 mSv for Implagraphy 1. These are 108.6, 54.1, 25.5, 18.2 and 6.2 times greater than panoramic examination (Cranex 3+) doses (0.023mSv). Conclusion: Cone beam CT machines recently developed in Korea, showed lower effective doses than conventional CT. Cone beam CT provides a lower dose and cost alternative to conventional CT, promising to revolutionize the practice of oral and maxillofacial radiology.