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Dose Measurements using Phantoms for Tube Voltage, Tube Current, Slice Thickness in MDCT.

Chang Lae LEE ; Hee Joung KIM ; Seong Su JEON ; So Ra NAM ; Hyo Min CHO ; Ji Young JUNG

Korean Journal of Medical Physics.2007;18(3):139-143.

The purpose of this study was to measure and evaluate radiation dose for MDCT parameters. Patient dose for various combination of MDCT parameters were experimentally measured, using MDCT (GE light speed plus 4 slice, USA), model 2026C electrometer (RADICAL 2026C, USA), standard Polymethylmethacrylate (PMMA) head and body CT dosimetry phantoms. In clinical situations, for a typical abdominal scan performed with MDCT at 120 kVp, 180 mAs, 20 mm collimation, and a pitch of 0.75, CTDIw, CTDIvol were measured as 20.2 mGy, 26.9 mGy, respectively. When scan length is assumed as 271.3 mm, DLP and measured effective dose of the abdominal would be calculated as 729.1 mGy cm, 10.9 mSv, respectively.
Head ; Humans ; Polymethyl Methacrylate

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The Evaluation for Attenuation Map using Low Dose in PET/CT System.

Sora NAM ; Hee Joung KIM ; Hyo Min CHO ; Ji young JUNG ; Chang Lae LEE ; Han Sang LIM ; Hoon Hee PARK

Korean Journal of Medical Physics.2007;18(3):134-138.

The current PET/CT system with high quality CT images not only increases diagnostic value by providing anatomic localization, but also shortens the acquisition time for attenuation correction than primary PET system. All commercially available PET/CT system uses the CT scan for attenuation correction instead of the transmission scan using radioactive source such as 137Cs, 68Ge. However the CT scan may substantially increase the patient dose. The purpose of this study was to evaluate quality of PET images reconstructed by CT attenuation map using various tube currents. In this study, images were acquired for 3D Hoffman brain phantom and cylindrical phantom using GE DSTe PET/CT system. The emission data were acquired for 10 min using phantoms after injecting 44.03 MBq of 18F-FDG. The CT images for attenuation map were acquired by changing tube current from 10 mA to 95 mA with fixed exposure time of 8 sec and fixed tube voltage of 140 kVp. The PET images were reconstructed using these CT attenuation maps. Image quality of CT images was evaluated by measuring SD (standard deviation) of cylindrical phantom which was filled with water and 18F-FDG solution. The PET images were evaluated by measuring the activity ratio between gray matter and white matter in Hoffman phantom images. SDs of CT images decrease by increasing tube current. When PET images were reconstructed using CT attenuation maps with various tube currents, the activity ratios between gray matter and white matter of PET images were almost same. These results indicated that the quality of the PET images using low dose CT data were comparable to the PET images using general dose CT data. Therefore, the use of low dose CT is recommended than the use of general dose CT, when the diagnostic high quality CT is not required. Further studies may need to be performed for other system, since this study is limited to the GE DSTe system used in this study.
Brain ; Fluorodeoxyglucose F18 ; Humans ; Positron-Emission Tomography and Computed Tomography* ; Tomography, X-Ray Computed ; Water

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A Monte Carlo Simulation for the Newly Developed Head-and-Neck IMRT Phantom: a Pilot Study.

Sei Kwon KANG ; Kwang Ho CHEONG ; Ra Hyeong JU ; Byung Chul CHO ; Do Hoon OH ; Su SSan KIM ; Kyoung Ju KIM ; Hoonsik BAE ; Youngyih HAN ; Eun Hyuk SHIN ; Sung Ho PARK ; Chunil LIM

Korean Journal of Medical Physics.2007;18(3):126-133.

A head-and-neck phantom was designed in order to evaluate remotely the quality of the delivery dose of intensity modulated radiation therapy (IMRT) in each institution. The phantom is homogeneous or inhomogeneous by interchanging the phantom material with the substructure like an air or bone plug. Monte Carlo simulations were executed for one beam and three beams to the phantom and compared with ion chamber and thermoluminescent dosimeter (TLD) measurements of which readings were from two independent institutions. For single beam, the ion chamber results and the MC simulations agreed to within about 2%. TLDs agreed with the MC results to within 2% or 7% according to which institution read the TLDs. For three beams, the ion chamber results showed -5% maximum discrepancy and those of TLDs were +2~+3%. The accuracy of the TLD readings should be increased for the remote dose monitoring. MC simulations are a valuable tool to acquire the reliability of the measurements in developing a new phantom.
Pilot Projects* ; Reading

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Evaluation of Geometric Correspondence of kV X-ray Images, Electric Portal Images and Digitally Reconstructed Radiographic Images.

Kwang Ho CHEONG ; Kyoung Joo KIM ; Byung Chul CHO ; Sei Kwon KANG ; Ra Hyeong JUH ; Hoon Sik BAE ; Tae Suk SUH

Korean Journal of Medical Physics.2007;18(3):118-125.

In this study we estimated a geometric correlation among digitally reconstructed radiographic image (DRRI), kV x-ray image (kVXI) from the On-Board Imager (OBI) and electric portal image (EPI). To verify geometric correspondence of DRRI, kVXI and EPI, specially designed phantom with indexed 6 ball bearings (BBs) were employed. After accurate setup of the phantom on a treatment couch using orthogonal EPIs, we acquired set of orthogonal kVXIs and EPIs then compared the absolute positions of the center of the BBs calculated at each phantom plane for kVXI and EPI respectively. We also checked matching result for obliquely incident beam (gantry angle of 315 degrees) after 2D-2D matching provided by OBI application. A reference EPI obtained after initial setup of the phantom was compared with 10 series of EPIs acquired after each 2D-2D matching. Imaginary setup errors were generated from -5 mm to 5 mm at each couch motion direction. Calculated positions of all center positions of the BBs at three different images were agreed with the actual points within a millimeter and each other. Calculated center positions of the BBs from the reference and obtained EPIs after 2D-2D matching agreed within a millimeter. We could tentatively conclude that the OBI system was mechanically quite reliable for image guided radiation therapy (IGRT) purpose.
Radiotherapy, Image-Guided

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A Comparison of Peripheral Doses Scattered from a Physical Wedge and an Enhanced Dynamic Wedge.

Jong Min PARK ; Hee Jung KIM ; Je Soon MIN ; Je Hee LEE ; Charn Il PARK ; Sung Joon YE

Korean Journal of Medical Physics.2007;18(3):107-117.

In order to evaluate the radio-protective advantage of an enhanced dynamic wedge (EDW) over a physical wedge (PW), we measured peripheral doses scattered from both types of wedges using a 2D array of ion-chambers. A 2D array of ion-chambers was used for this purpose. In order to confirm the accuracy of the device, we first compared measured profiles of open fields with the profiles calculated by our commissioned treatment planning system. Then, we measured peripheral doses for the wedge angles of 15 degrees, 30 degrees, 45 degrees, and 60 degrees at source to surface distances (SSD) of 80 cm and 90 cm. The measured points were located at 0.5 cm depth from 1 cm to 5 cm outside of the field edge. In addition, the measurements were repeated by using thermoluminescence dosimeters (TLD). The peripheral doses of EDW were (1.4% to 11.9%) lower than those of PW (2.5% to 12.4%). At 15 MV energy, the average peripheral doses of both wedges were 2.9% higher than those at 6MV energy. At a small SSD (80 cm vs. 90 cm), peripheral dose differences were more recognizable. The average peripheral doses to the heel direction were 0.9% lower than those to the toe direction. The results from the TLD measurements confirmed these findings with similar tendency. Dynamic wedges can reduce unnecessary scattered doses to normal tissues outside of the field edge in many clinical situations. Such an advantage is more profound in the treatment of steeper wedge angles, and shorter SSD.
Heel ; Silver Sulfadiazine ; Toes

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Estimation of CyberKnife Respiratory Tracking System Using Moving Phantom.

Jae Hyuk SEO ; Young Nam KANG ; Ji Sun JANG ; Hun Joo SHIN ; Ji Young JUNG ; Byong Ock CHOI ; Ihl Bohng CHOI ; Dong Joon LEE ; Soo Il KWON ; Jong Soo LIM

Korean Journal of Medical Physics.2009;20(4):324-330.

In this study, we evaluated accuracy and usefulness of CyberKnife Respiratory Tracking System (SynchronyTM, Accuray, USA) about a moving during stereotactic radiosurgery. For this study, we used moving phantom that can move the target. We also used Respiratory Tracking System called Synchrony of the Cyberknife in order to track the moving target. For treatment planning of the moving target, we obtained an image using 4D-CT. To measure dose distribution and point dose at the moving target, ion chamber (0.62 cc) and gafchromic EBT film were used. We compared dose distribution (80% isodose line of prescription dose) of static target to that of moving target in order to evaluate the accuracy of Respiratory Tracking System. We also measured the point dose at the target. The mean difference of synchronization for TLS (target localization system) and Synchrony were 11.5+/-3.09 mm for desynchronization and 0.14+/-0.08 mm for synchronization. The mean difference between static target plan and moving target plan using 4D CT images was 0.18+/-0.06 mm. And, the accuracy of Respiratory Tracking System was less 1 mm. Estimation of usefulness in Respiratory Tracking System was 17.39+/-0.14 mm for inactivity and 1.37+/-0.11 mm for activity. The mean difference of absolute dose was 0.68+/-0.38% in static target and 1.31+/-0.81% in moving target. As a conclusion, when we treat about the moving target, we consider that it is important to use 4D-CT and the Respiratory Tracking System. In this study, we confirmed the accuracy and usefulness of Respiratory Tracking System in the Cyberknife.
Four-Dimensional Computed Tomography ; Prescriptions ; Radiosurgery ; Track and Field

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The Study on the Use of a Cylindrical Ionization Chamber for the Calibration of a 6 MeV Electron Beam.

Seong Hoon KIM ; Hyundo HUH ; Sang Hyun CHOI ; Jinho CHOI ; Hyeog Ju KIM ; Chunil LIM ; Dong Oh SHIN

Korean Journal of Medical Physics.2009;20(4):317-323.

The standard dosimetry systems based on an absorbed dose to water recommend to use a planeparallel chamber for the calibration of such a low-megavoltage electron beam as a nominal energy of 6 MeV. For this energy ranges of an electron beam a cylindrical chamber should not be used for the routinely regular beam calibration, but the feasibility of the temporary use of a cylindrical chamber was studied to give temporary solutions for special situations users meet. The PTW30013 chambers and the electron beam quality of R(50)=2.25 g/cm2 were selected for this study. 10 PTW30013 chambers, a cylindrical type of chamber, were calibrated in KFDA, the secondary standards dosimetry laboratories, and given the absorbed dose-to-water calibration factors, respectively. A "temporary" kappa(Q,Q0) for each chamber were calculated using the absorbed dose determined by a cross-calibrated planeparallel chamber, with the result of an average 0.9352 for 10 chambers. This value for PTW30013 chamber was used to determine an absorbed dose to water at the reference depth. The absorbed doses determined by PTW30013 chambers were in an agreement within 2% with that by ROOS chamber. In a certain situation where a cylindrical chamber be used instead of a planeparellel chamber, the value of 0.9352 might be useful to determine an absorbed dose to water in the same beam quality of electron beam as this study.
Calibration ; Electrons ; Water

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Evaluation the Output Dose of Linear Accelerator Photon Beams by Blind Test with Dose Characteristics of LiF:Mg,Cu,P TLD.

Tae Jin CHOI ; Ho Joon LEE ; Ji Won YIE ; Young Gi OH ; Jin Hee KIM ; Ok Bae KIM

Korean Journal of Medical Physics.2009;20(4):308-316.

To achieve the accurate evaluation of given absorbed dose from output dose of linear accelerator photon beam through investigate the characteristics of LiF:Mg,Cu,P TLD powder. This experimental TL phosphor is performed with a commercial LiF:Mg,Cu,P powder (Supplied by PTW) and TL reader (LTM, France). The TLD was exposed to 6 MV X rays of linear accelerator photon beam with range 15 to 800 cGy in blind dose at two hospitals. The dose evaluation of TLD was through the experimental algorithms which were dose dependency, dose rate dependency, fading and powder weight dependency. The glow curve has shown the three peaks which are 110, 183 and 232 degrees of heating temperature and the main dosimetric peak showed highest TL response at 232 high temperature. In this experiments, the LiF:Mg,Cu,P phosphor has shown the 2.5 eV of electron trap energy with a second order. This experiments guided the dose evaluation accuracy is within 1% +2.58% of discrepancy. The TLD powder of LiF:Mg,Cu,P was analyzed to dosimetric characterists of electron captured energy and order by glow shape, and dose-TL response curve guided the accuracy within 1.0+2.58% of output dose discrepancy.
Dependency (Psychology) ; Electrons ; Heating ; Hot Temperature ; Particle Accelerators

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MR T2 Map Technique: How to Assess Changes in Cartilage of Patients with Osteoarthritis of the Knee.

Jae Hwan CHO ; Cheol Soo PARK ; Sun Yeob LEE ; Bo Hui KIM

Korean Journal of Medical Physics.2009;20(4):298-307.

By using the MR T2 map technique, this study intends, first, to measure the change of T2 values of cartilage between healthy people and patients with osteoarthritis and, second, to assess the form and the damage of cartilage in the knee-joint, through which this study would consider the utility of the T2 map technique. Thirty healthy people were selected based on their clinical history and current status and another thirty patients with osteoarthritis of the knee who were screened by simple X-ray from November 2007 to December 2008 were selected. Their T2 Spin Echo (SE hereafter) images for the cartilage of the knee joint were collected by using the T2 SE sequence, one of the multi-echo methods (TR: 1,000 ms; TE values: 6.5, 13, 19.5, 26, 32.5. 40, 45.5, 52). Based on these images, the changes in the signal intensity (SI hereafter) for each section of the cartilage of the knee joint were measured, which yielded average values of T2 through the Origin 7.0 Professional (Northampton, MA 01060 USA). With these T2s, the independent samples T-test was performed by SPSS Window version 12.0 to run the quantitative analysis and to test the statistical significance between the healthy group and the patient group. Closely looking at T2 values for each anterior and lateral articular cartilage of the sagittal plane and the coronal plane, in the sagittal plane, the average T2 of the femoral cartilage in the patient group with arthritis of the knee (42.22+/-2.91) was higher than the average T2 of the healthy group (36.26+/-5.01). Also, the average T2 of the tibial cartilage in the patient group (43.83+/-1.43) was higher than the average T2 in the healthy group (36.45+/-3.15). In the case of the coronal plane, the average T2 of the medial femoral cartilage in the patient group (45.65+/-7.10) was higher than the healthy group (36.49+/-8.41) and so did the average T2 of the anterior tibial cartilage (i.e., 44.46+/-3.44 for the patient group vs. 37.61+/-1.97 for the healthy group). As for the lateral femoral cartilage in the coronal plane, the patient group displayed the higher T2 (43.41+/-4.99) than the healthy group did (37.64+/-4.02) and this tendency was similar in the lateral tibial cartilage (i.e., 43.78+/-8.08 for the patient group vs. 36.62+/-7.81 for the healthy group). Along with the morphological MR imaging technique previously used, the T2 map technique seems to help patients with cartilage problems, in particular, those with the arthritis of the knee for early diagnosis by quantitatively analyzing the structural and functional changes of the cartilage.
Arthritis ; Cartilage ; Cartilage, Articular ; Early Diagnosis ; Humans ; Knee ; Knee Joint ; Osteoarthritis ; Osteoarthritis, Knee

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Study on the Small Fields Dosimetry for High Energy Photon-based Radiation Therapy.

Hae Sun JEONG ; Youngyih HAN ; Oyeon KUM ; Chan Hyeong KIM

Korean Journal of Medical Physics.2009;20(4):290-297.

In case of radiation treatment using small field high-energy photon beams, an accurate dosimetry is a challenging task because of dosimetrically unfavorable phenomena such as dramatic changes of the dose at the field boundaries, dis-equilibrium of the electrons, and non-uniformity between the detector and the phantom materials. In this study, the absorbed dose in the phantom was measured by using an ion chamber and a diode detector widely used in clinics. GAFCHROMIC(R) EBT films composed of water equivalent materials was also evaluated as a small field detector and compared with ionchamber and diode detectors. The output factors at 10 cm depth of a solid phantom located 100 cm from the 6 MV linear accelerator (Varian, 6 EX) source were measured for 6 field sizes (5x5 cm2, 2x2 cm2, 1.5x1.5 cm2, 1x1 cm2, 0.7x0.7 cm2 and 0.5x0.5 cm2). As a result, from 5x5 cm2 to 1.5x1.5 cm2 field sizes, absorbed doses from three detectors were accurately identified within 1%. Wheres, the ion chamber underestimated dose compared to other detectors in the field sizes less than 1x1 cm2. In order to correct the observed underestimation, a convolution method was employed to eliminate the volume averaging effect of an ion chamber. Finally, in 1x1 cm2 field the absorbed dose with a diode detector was about 3% higher than that with the EBT film while the dose with the ion chamber after volume correction was 1% lower. For 0.5x0.5 cm2 field, the dose with the diode detector was 1% larger than that with the EBT film while dose with volume corrected ionization chamber was 7% lower. In conclusion, the possiblity of GAFCHROMIC(R) EBT film as an small field dosimeter was tested and further investigation will be proceed using Monte Calro simulation.
Electrons ; Particle Accelerators ; Water

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