• Radiation Oncology Journal
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• v.24 no.4
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• pp.285-293
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• 2006

$\underline{Purpose}$: This study was to search the optimal slice thickness of computed tomography (CT) in an intensity modulated radiation therapy plan through changing the slice thickness and comparing the change of the calculated absorbed dose with measured absorbed dose. $\underline{Materials\;and\;Methods}$: An intensity modulated radiation therapy plan for a head and neck cancer patient was done, first of all. Then CT with various ranges of slice thickness ($0.125{\sim}1.0\;cm$) for a head and neck anthropomorphic phantom was done and the images were reconstructed. The plan parameters obtained from the plan of the head and neck cancer patient was applied into the reconstructed images of the phantom and then absorbed doses were calculated. Films were inserted into the phantom, and irradiated with 6 MV X-ray with the same beam data obtained from the head and neck cancer patient. Films were then scanned and isodoses were measured with the use of film measurement software and were compared with the calculated isodeses. $\underline{Results}$: As the slice thickness of CT decreased, the volume of the phantom and the maximum absorbed dose increased. As the slice thickness of CT changed from 0.125 to 1.0 cm, the maximum absorbed dose changed ${\sim}5%$. The difference between the measured and calculated volume of the phantom was small ($3.7{\sim}3.8%$) when the slice thickness of CT was 0.25 cm or less. The difference between the measured and calculated dose was small ($0.35{\sim}1.40%$) when the slice thickness of CT was 0.25 cm or less. $\underline{Conclusion}$: Because the difference between the measured and calculated dose in a head and neck phantom was small and the difference between the measured and calculated volume was small when the slice thickness of CT was 0.25 cm or less, we suggest that the slice thickness of CT should be 0.25 cm or less for an optimal intensity modulated radiation therapy plan.

• Journal of the Korean Society of Radiology
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• v.7 no.1
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• pp.45-50
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• 2013

Non-invasive technique CT, called automated computed tomography, is used to detect lesion of a patient when diagnosing human body. Information obtained from CT plays an important role in assembling 3 dimensional images. Recently, new equipment, operated by CT, is required which can be appliable to physical and biological research. In accordance to this quest, micro-CT is invented that produce more detail and concrete information. Images supplied by CT are even more detailed and concrete, so it contributes much to the development of biology and polymer material engineering field. However, there has been little reliable reports regarding measuring information of space dose distribution about exposure dose limit of users operating micro-CT. In addition, little reports regarding space dose distribution of exposure has been known about unwanted diffraction light produced by usage of micro-CT. The exterior of micro-CT is covered by lead, which is for removing exposure of diffraction light. Thus, even if it is good enough to prevent exposure of diffraction light, consistent management of equipment will be required as time goes by and equipment are getting old as well. We measured space dose distribution regarding exposure of diffraction light of users operating micro-CT directly. Therefore, we suggest that proper management should be necessary for users operating micro-CT not to be exposed by unwanted diffraction light.

• Journal of radiological science and technology
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• v.31 no.2
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• pp.171-175
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• 2008

The aim of this study is to assess the dose reduction of eye lens and availability of bismuth garments resulting from the use of radioprotective bismuth garments to shield the eyes of patients undergoing head CT. Rando phantom and TLDs were used to determine the amount of dose reduction by bismuth shielding of the eye in the following simulated CT scans : (a) scanning of the head including orbits, (b) scanning of the whole head, and (c) $20^{\circ}$ angled scanning of the head excluding orbits. The average dose reduction of eye lens was 43.2%, 36.0% and 1.4% for the three CT scans listed above. Significant reduction in the eye lens dose was achieved by using superficial orbital bismuth shielding during head CT scans. However, bismuth shields should not be used for the patients when their eyes are excluded from the primarily exposed region.

• Journal of radiological science and technology
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• v.32 no.3
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• pp.307-312
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• 2009

The purpose of our study was to determine the eyeradiation dose when performing routine multi-detector computed tomography (MDCT). We also evaluated dose reduction and the effect on image quality of using a bismuth eye shield when performing head MDCT. Examinations were performed with a 64MDCT scanner. To compare the shielded/unshielded lens dose, the examination was performed with and without bismuth shielding in anthropomorphic phantom. To determine the average lens radiation dose, we imaged an anthropomorphic phantom into which calibrated photoluminescence glass dosimeter (PLD) were placed to measure the dose to lens. The phantom was imaged using the same protocol. Radiation doses to the lens with and without the lensshielding were measured and compared using the Student t test. In the qualitative evaluation of the MDCT scans, all were considered to be of diagnostic quality. We did not see any differences in quality between the shielded and unshielded brain. The mean radiation doses to the eyewith the shield and to those without the shield were 21.54 versus 10.46 mGy, respectively. The lens shield enabled a 51.3% decrease in radiation dose to the lens. Bismuth in-plane shielding for routine eye and head MDCT decreased radiation dose to the lenswithout qualitative changes in image quality. The other radiosensitive superficial organs specifically must be protected with shielding.

• The Journal of the Korea Contents Association
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• v.13 no.11
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• pp.768-777
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• 2013

The purpose of this study is to minimize radiation exposure to the workers and public members during CT examination. The objects are seven of the CT rooms in university hospitals and four of the CT rooms in clinics located in Busan and Gyung-nam area. The places of measurement for radiation leakage are 1) 3 m above the ground of shielding wall in the control room 2) particular space in the control room 3) worker's gate in the control room 4) the patient gate. Its values were calculated maximum leakage radiation per week(MLRW). As a result, the worker's gate of M clinic displayed the highest dose. When it was calculated by MLRW in classic method, it showed 1) $5.97{\pm}0.23$, 2) $0.50{\pm}0.02$, 3) $10.00{\pm}0.11$, 4) $2.37{\pm}0.47$ mR/week. All of them did not exceed limit for maximum permissible dose per week(MPDW). However, When MLRW of M clinic was calculated by empirical method, its value displayed $118.31{\pm}17.72$ mR/week.(MPDW>100 mR/week). Radiation leakage influenced in the control room(p<0.05). Therefore, The way of calculating MLRW must be developed and shielding wall in control room is designed 3 m above the ground for reducing dangerous of leakage radiation.

• Progress in Medical Physics
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• v.23 no.1
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• pp.62-69
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• 2012

The dose re-calculation process using Megavoltage cone-beam CT images is inevitable process to perform the Adaptive Radiation Therapy (ART). The purpose of this study is to improve dose re-calculation accuracy using MVCBCT images by applying intensity calibration method and three dimensional rigid body transform and filtering process. The three dimensional rigid body transform and Gaussian smoothing filtering process to MVCBCT Rando phantom images was applied to reduce image orientation error and the noise of the MVCBCT images. Then, to obtain the predefined modification level for intensity calibration, the cheese phantom images from kilo-voltage CT (kV CT), MVCBCT was acquired. From these cheese phantom images, the calibration table for MVCBCT images was defined from the relationship between Hounsfield Units (HUs) of kV CT and MVCBCT images at the same electron density plugs. The intensity of MVCBCT images from Rando phantom was calibrated using the predefined modification level as discussed above to have the intensity of the kV CT images to make the two images have the same intensity range as if they were obtained from the same modality. Finally, the dose calculation using kV CT, MVCBCT with/without intensity calibration was applied using radiation treatment planning system. As a result, the percentage difference of dose distributions between dose calculation based on kVCT and MVCBCT with intensity calibration was reduced comparing to the percentage difference of dose distribution between dose calculation based on kVCT and MVCBCT without intensity calibration. For head and neck, lung images, the percentage difference between kV CT and non-calibrated MVCBCT images was 1.08%, 2.44%, respectively. In summary, our method has quantitatively improved the accuracy of dose calculation and could be a useful solution to enhance the dose calculation accuracy using MVCBCT images.

• Journal of radiological science and technology
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• v.34 no.2
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• pp.105-116
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• 2011

In this study, we present the measurements of effective dose from CT of head & neck region. A series of dose measurements in anthropomorphic Rando phantom was conducted using a radio photoluminescent glass rod dosimeter to evaluate effective doses of organs of head and neck region from the patient. The experiments were performed with respect to four anatomic regions of head & neck: optic nerve, pons, cerebellum, and thyroid gland. The head & neck CT protocol was used in the single scan (Brain, 3D Facial, Temporal, Brain Angiography and 3D Cervical Spine) and the multiple scan (Brain+Brain Angiography, Brain+3D Facial, Brain+Temporal, Brain+3D Cervical spine, Brain+3D Facial+Temporal, Brain+3D Cervical Spine+Brain Angiography). The largest effective dose was measured at optic nerve in Brain CT and Brain Angiography. The largest effective dose was delivered to the thyroid grand in 3D faical CT and 3D cervical spine, and to the pons in Temporal CT. In multiple scans, the higher effective dose was measured in the thyroid grand in Brain+3D Facial, Brain+3D Cervical Spine, Brain+3D Facial+Temporal and Brain+3D Cervical Spine+Brain Angiography. In addition, the largest effective dose was delivered to the cerebellum in Brain CT+Brain Angiography CT and higher effective dose was delivered to the pons in Brain+Temporal CT. The results indicate that in multiple scan of Brain+3D Cervical Spine+Brain Angiography, effective dose was 2.52 mSv. This is significantly higher dose than the limitation of annual effective dose of 1 mSv. The effective dose to the optic nerve was 0.31 mSv in Brain CT, which shows a possibility of surpassing the limitation of 1 mSv by furthre examination. Therefore, special efforts should be made in clinical practice to reduce dose to the patients.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.2
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• pp.33-41
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• 2017

Objectives: The aim of this study is to evaluate the reproducibility and usefulness of the images through the fusion of CT(Computed tomography) and MRI(Magnetic resonance imaging) using a self-manufactured phantom. We will also compare and analyze the target dose from acquired images. Materials and Methods: Using a self-manufactured phantom, CT images and MRI images are acquired by 1.5T and 3.0T of different magnetic fields. The reproducibility of the size and volume of the small holes present in the phantom is compared through the image from CT and 1.5T and 3.0T MRI, and dose changes are compared and analyzed on any target. Results: 13 small hole diameters were a maximum 31 mm and a minimum 27.54 mm in the CT scan and the were measured within an average of 29.28 mm 1 % compared to actual size. 1.5 T MRI images showed a maximum 31.65 mm and a minimum 24.3 mm, the average is 28.8 mm, which is within 1 %. 3.0T MRI images showed a maximum 30.2 mm and a minimum 27.92 mm, the average is 29.41 mm, which is within 1.3 %. The dose changes in the target were 95.9-102.1 % in CT images, 93.1-101.4 % in CT-1.5T MRI fusion images, and 96-102 % in CT-3.0T MRI fusion images. Conclusion: CT and MRI are applied with different algorithms for image acquisition. Also, since the organs of the human body have different densities, image distortion may occur during image acquisition. Because these inaccurate images description affects the volume range and dose of the target, accurate volume and location of the target can prevent unnecessary doses from being exposed and errors in treatment planning. Therefore, it should be applied to the treatment plan by taking advantage of the image display algorithm possessed by CT and MRI.

• Progress in Medical Physics
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• v.23 no.4
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• pp.292-302
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• 2012

The patient dose in advanced radiotherapy techniques is an important issue. These methods should be evaluated to reduce the dose in diagnostic imaging for radiotherapy. Especially, the Computed Tomography in radiotherapy has been used widely; hence the CT was evaluated for dose and image in this study. The evaluations for dose and image were done in equal condition due to compare the dose and image simultaneously. Furthermore, the possibility of dose and image evaluations by using the Monte Carlo simulation MCNPX was confirmed. We made the iterative reconstruction for low dose CT image to elevate image quality with Maximum Likelihood Expectation Maximization; MLEM. The system we developed is expected to be used not only to reduce the patient dose in radiotherapy, also to evaluate the overall factors of image modalities in industrial research.

• Progress in Medical Physics
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• v.21 no.3
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• pp.246-252
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• 2010

The purpose of this study provides measurements of radiation dose from MDCT of head, chest, abdomen and pelvic examinations. A series of dose quantities that are measured of patient weight to compare the dose received during MDCT examinations. Data collected included: weight together with CT dose descriptors, volume CT dose index (CTDIvol) and dose length product (DLP). The effective dose was also estimated and served as collective dose estimation data. Data from 1,774 adult patients attending for a CT examination of the head (n=520) or chest (n=531) or abdomen (n=724) was obtained from spiral CT units using a same CT protocol. Mean values of CTDIvol was a range of 48.6 mGy for head and 6.9, 10.5 mGy for chest, abdomen examinations, respectively. And mean values of DLP was range of 1,604 $mGy{\cdot}cm$ for head, 250 $mGy{\cdot}cm$ for chest, 575 $mGy{\cdot}cm$ for abdomen examinations, respectively. Mean effective dose values for head, chest, abdominal CT were 3.6, 4.2, and 8.6 mSv, respectively. The degree of CTDIvol and DLP was a positive correlation with weight. And there was a positive correlation for weight versus CTDIvol ($r^2$=0.62), DLP ($r^2$=0.694) in chest. And head was also positive correlation with weight versus CTDIvol ($r^2$=0.691), DLP ($r^2$=0.741). We conclude that CTDIvol and DLP is an important determinant of weight within the CT examinations. The results for this study suggest that CT protocol should be tailored according to patient weight.