검색
검색 팝업 닫기

Ex) Article Title, Author, Keywords

Articles

Archives
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 277 \ 134

    Improvement of Analytic Reconstruction Algorithms Using a Sinogram Interpolation Method for Sparse-angular Sampling with a Photon-counting Detector

    Dohyeon Kim, Byungdu Jo, Su-Jin Park, Hyemi Kim, Hee-Joung Kim

    Abstract
    Sparse angular sampling has been studied recently owing to its potential to decrease the radiation exposure from computed tomography (CT). In this study, we investigated the analytic reconstruction algorithm in sparse angular sampling using the sinogram interpolation method for improving image quality and computation speed. A prototype of the spectral CT system, which has a 64-pixel Cadmium Zinc Telluride (CZT)-based photon-counting detector, was used. The source-to-detector distance and the source-to-center of rotation distance were 1,200 and 1,015 mm, respectively. Two energy bins (23∼33 keV and 34∼44 keV) were set to obtain two reconstruction images. We used a PMMA phantom with height and radius of 50.0 mm and 17.5 mm, respectively. The phantom contained iodine, gadolinium, calcification, and lipid. The Feld-kamp-Davis-Kress (FDK) with the sinogram interpolation method and Maximum Likelihood Expectation Maximization (MLEM) algorithm were used to reconstruct the images. We evaluated the signal-to-noise ratio (SNR) of the materials. The SNRs of iodine, calcification, and liquid lipid were increased by 167.03%, 157.93%, and 41.77%, respectively, with the 23∼33 keV energy bin using the sinogram interpolation method. The SNRs of iodine, calcification, and liquid state lipid were also increased by 107.01%, 13.58%, and 27.39%, respectively, with the 34∼44 keV energy bin using the sinogram interpolation method. Although the FDK algorithm with the sinogram interpolation did not produce better results than the MLEM algorithm, it did result in comparable image quality to that of the MLEM algorithm. We believe that the sinogram interpolation method can be applied in various reconstruction studies using the analytic reconstruction algorithm. Therefore, the sinogram interpolation method can improve the image quality in sparse-angular sampling and be applied to CT applications.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 423 \ 139

    Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

    Kyung Hwan Chang, Yunseo Ji, Jungwon Kwak, Sung Woo Kim, Chiyoung Jeong, Byungchul Cho, Jin-hong Park, Sang Min Yoon, Seung Do Ahn, Sang-wook Lee

    Abstract
    This study is to evaluate the dosimetric impact of dosimetric leaf gap (DLG) and transmission factor (TF) at different measurement depths and field sizes for high definition multileaf collimator (HD MLC). Consequently, its clinical implication on dose calculation of treatment planning system was also investigated for pancreas stereotactic body radiation therapy (SBRT). The TF and DLG were measured at various depths (5, 8, 10, 12, and 15 cm) and field sizes (6×6, 8×8, and 10×10 cm2) for various energies (6 MV, 6 MV FFF, 10 MV, 10 MV flattening filter free [FFF], and 15 MV). Fifteen pancreatic SBRT cases were enrolled in the study. For each case, the dose distribution was recomputed using a reconfigured beam model of which TF and DLG was the closest to the patient geometry, and then compared to the original plan using the results of dose-volume histograms (DVH). For 10 MV FFF photon beam, its maximum difference between 2 cm and 15 cm was within 0.9% and it is increased by 0.05% from 6×6 cm2 to 10×10 cm2 for depth of 15 cm. For 10 MV FFF photon beam, the difference in DLG between the depth of 5 cm and 15 cm is within 0.005 cm for all field sizes and its maximum difference between field size of 6×6 cm2 and 10×10 cm2 is 0.0025 cm at depth of 8 cm. TF and DLG values were dependent on the depth and field size. However, the dosimetric difference between the original and recomputed doses were found to be within an acceptable range (<0.5%). In conclusion, current beam modeling using single TF and DLG values is enough for accurate dose calculation.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 198 \ 170

    Feasibility Study of Robotics-based Patient Immobilization Device for Real-time Motion Compensation

    Hyekyun Chung, Seungryong Cho, Byungchul Cho

    Abstract
    Intrafractional motion of patients, such as respiratory motion during radiation treatment, is an important issue in image-guided radiotherapy. The accuracy of the radiation treatment decreases as the motion range increases. We developed a control system for a robotic patient immobilization system that enables to reduce the range of tumor motion by compensating the tumor motion. Fusion technology, combining robotics and mechatronics, was developed and applied in this study. First, a small-sized prototype was established for use with an industrial miniature robot. The patient immobilization system consisted of an optical tracking system, a robotic couch, a robot controller, and a control program for managing the system components. A multi speed and position control mechanism with three degrees of freedom was designed. The parameters for operating the control system, such as the coordinate transformation parameters and calibration parameters, were measured and evaluated for a prototype device. After developing the control system using the prototype device, a feasibility test on a full-scale patient immobilization system was performed, using a large industrial robot and couch. The performances of both the prototype device and the realistic device were evaluated using a respiratory motion phantom, for several patterns of respiratory motion. For all patterns of motion, the root mean squared error of the corresponding detected motion trajectories were reduced by more than 40%. The proposed system improves the accuracy of the radiation dose delivered to the target and reduces the unwanted irradiation of normal tissue.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 437 \ 128

    Optimization of Energy Modulation Filter for Dual Energy CBCT Using Geant4 Monte-Carlo Simulation

    Eun Bin Ju, So Hyun Ahn, Sang Gyu Choi, Rena Lee

    Abstract
    Dual energy computed tomography (DECT) is used to classify two materials and quantify the mass density of each material in the human body. An energy modulation filter based DECT could acquire two images, which are generated by the low- and high-energy photon spectra, in one scan, with one tube and detector. In the case of DECT using the energy modulation filter, the filter should perform the optimization process for the type of materials and thicknesses for generating two photon spectra. In this study, Geant4 Monte-Carlo simulation toolkit was used to execute the optimization process for determining the property of the energy modulation filter. In the process, various materials used for the energy modulation filter are copper (Cu, 8.96 g/cm3), niobium (Nb, 8.57 g/cm3), stannum (Sn, 7.31 g/cm3), gold (Au, 19.32 g/cm3), and lead (Pb, 11.34 g/cm3). The thickness of the modulation filter varied from 0.1 mm to 1.0 mm. To evaluate the overlap region of the low- and high-energy spectrum, Geant4 Monte-Carlo simulation is used. The variation of the photon flux and the mean energy of photon spectrum that passes through the energy modulation filter are evaluated. In the primary photon spectrum of 80 kVp, the optimal modulation filter is a 0.1 mm lead filter that can acquire the same mean energy of 140 kVp photon spectrum. The lead filter of 0.1 mm based dual energy CBCT is required to increase the tube current 4.37 times than the original tube current owing to the 77.1% attenuation in the filter.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 264 \ 142

    Comparative Analysis of Terminology and Classification Related to Risk Management of Radiotherapy

    Yoonjin Oh, Dong Wook Kim, Dong Oh Shin, Jihye Koo, Soon Sung Lee, Sang Hyoun Choi, Sohyun Ahn, Dong-wook Park

    Abstract
    We analyzed the terminology and classification related to the risk management of radiation treatment overseas to establish the terminology and classification system for Korea. This study investigated the terminology and classification for radiotherapy risk management through overseas research materials from related organizations and associations, including the IAEA, WHO, British group, EC, and AAPM. Overseas risk management commonly uses the terms “near miss”, “incident”, and “adverse event”, classified according to the degree of severity. However, several organizations have ambiguous terminologies. They use the term “near miss” for events such as a near event, close call, and good catch; the term “incident” for an event; and the term “adverse event” for the likes of an accident and an event. In addition, different organizations use different classifications: a “near miss” is generally classified as “incident” in most cases but not classified as such in BIR et al. Confusion might also be caused by the disunity of the terminology and classification, and by the ambiguity of definitions. Patient safety management of medical institutions in Korea uses the terms “near miss”, “adverse event”, and “sentinel event”, which it classifies into eight levels according to the severity of risk to the patient. Therefore, the terminology and classification for radiotherapy risk management based on the patient safety management of medical institutions in Korea will help in improving the safety and quality of radiotherapy.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 373 \ 179

    A Study of Institutional Status of Risk Management for Radiotherapy in Foreign Country

    Soon Sung Lee, Dong Oh Shin, Young Hoon Ji, Dong Wook Kim, Sohyoun An, Dong-Wook Park, Gyu Suk Cho, Kum-Bae Kim, Jihye Koo, Yoon-Jin Oh, Sang Hyoun Choi

    Abstract
    With the development in field of industry and medicine, new machines and techniques are being launched. Moreover, the complexity of the techniques is associated to an increasing risk of incident. Especially, a small error in radiotherapy can lead to a serious patient-related incident, risk management is necessary in radiotherapy in order to reduce the risk of incident. However, in field of radiotherapy, there are no legally binding clauses for risk management and there is an absence of risk management systems at an institutional level. Therefore, we analyzed institutional status of risk management, reporting & classification systems, and risk assessment & analysis in 31 countries. For risk management and reporting systems, 65% of countries investigated had legislation or regulations; however, only 35% of countries used classification systems. It was found that 43% more countries had legislation for risk management in healthcare than those for radiotherapy; 19% more countries had reporting systems for healthcare than those for radiotherapy. For classification systems, 60% more countries had legislation, recommendation, and guidelines in the field of radiotherapy than those for healthcare. Recently, international institutes have published several reports for risk management and patient safety in radiotherapy, owing to which, countries adopting risk management for radiotherapy will gradually increase. Before adopting risk management in Korea, we should precisely understand the procedures and functions of risk management, in order to increase efficiency of risk management because classification & reporting system and risk assessment & analysis are connected organically, and institutional management is needed for high quality of risk management in Korea.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 214 \ 145

    Analysis of Trends in Dose through Evaluation of Spatial Dose Rate and Surface Contamination in Radiation-Controlled Area and Personal Exposed Dose of Radiation Worker at the Korea Institute of Radiological and Medical Sciences (KIRAMS)

    Bu Hyung Lee, Sung Ho Kim, Soo Il Kwon, Jae Seok Kim, Gi-sub Kim, Min Seok Park, Seungwoo Park, Haijo Jung

    Abstract
    As the probability of exposure to radiation increases due to an increase in the use of radioisotopes and radiation generators, the importance of a radiation safety management field is being highlighted. We intend to help radiation workers with exposure management by identifying the degree of radiation exposure and contamination to determine an efficient method of radiation safety management. The personal exposure doses of the radiation workers at the Korea Institute of Radiological & Medical Sciences measured every quarter during a five-year period from Jan. 1, 2011 till Dec. 31, 2015 were analyzed using a TLD (thermoluminescence dosimeter). The spatial dose rates of radiation-controlled areas were measured using a portable radioscope, and the level of surface contamination was measured at weekly intervals using a piece of smear paper and a low background alpha/beta counter. Though the averages of the depth doses and the surface doses in 2012 increased from those in 2011 by about 14%, the averages were shown to have decreased every year after that. The exposure dose of 27 mSv in 2012 increased from that in 2011 in radiopharmaceutical laboratories and, in the case of the spatial dose rate, the rate of decrease in 2012 was shown to be similar to the annual trend of the whole institute. In the case of the surface contamination level, as the remaining radiation-controlled area with the exception of the I-131 treatment ward showed a low value less than 1.0 kBq/m², the annual trend of the I-131 treatment ward was shown to be similar to that of the entire institute. In conclusion, continuous attention should be paid to dose monitoring of the radiation-controlled areas where unsealed sources are handled and the workers therein.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 201 \ 160

    Analysis of Air Discharge and Disused Air Filters in Radioisotope Production Facility

    Sung Ho Kim, Bu Hyung Lee, Soo Il Kwon, Jae Seok Kim, Gi-sub Kim, Min Seok Park, Haijo Jung

    Abstract
    When air discharged from a radioisotope production facility is contaminated with radiation, the public may be exposed to radiation. The objective of this study is to manage such radiation exposure. We measured the airborne radioactivity concentration at a 30 MeV cyclotron radioisotope production facility to assess whether the exhaust gas was contaminated. Additionally, we investigted the radioactive contamination of the air filter for efficient air purification and radiation safety control. To measure the airborne radiation concentration, specimens were collected weekly for 4 h after the beginning of the radioisotope production. Regarding the air purifier, five specimens were collected at different positions of each filter—pre-filter, high-efficiency particulate air filter, and charcoal filter—installed in the cyclotron production room. The concentrations of F-18, I-123, I-131, and Tl-201 generated in the radioiodine production room were 13.5 Bq/m3, 27.0 Bq/m3, 0.10 Bq/m3, and 11.5 Bq/m3, respectively; the concentrations of F-18, I-123, and I-131 produced in the radioisotope production room were 0.05 Bq/m3, 16.1 Bq/m3, and 0.45 Bq/m3, correspondingly; and those of F-18, I-123, I-131, and Tl-201 generated in the accelerator room were 2.07 Bq/m3, 53.0 Bq/m3, 0.37 Bq/m3, and 0.15 Bq/m3, respectively. The maximum radiation concentration of I-123 generated in the radioiodine production room was 1,820 Bq/g, which can be disposed after 2 days. The maximum radiation concentration of Tl-202 generated in the radioisotope production room was 205 Bq/g, and this isotope must be stored for 53 days. The I-123 generated in the radioiodine production room had a maximum concentration of 1,530 Bq/g and must be stored for 2 days. The maximum radiation concentration of Na-22 generated in the radioisotope production room was 0.18 Bq/g and this isotope must be disposed after 827 days. To manage the exhaust, the efficiency of air purification must be enhanced by selecting an air purifier with a long life and determining the appropriate replacement time by examining the differential pressure through systematic measurements of the airborne radiation contamination level.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 291 \ 184

    Secondary Neutron Dose Measurement for Proton Line Scanning Therapy

    Chaeyeong Lee, Sangmin Lee, Kwangzoo Chung, Youngyih Han, Yong Hyun Chung, Jin Sung Kim

    Abstract
    Proton therapy is increasingly being actively used in the treatment of cancer. In contrast to photons, protons have the potential advantage of delivering higher doses to the cancerous tissue and lower doses to the surrounding normal tissue. However, a range shifter is needed to degrade the beam energy in order to apply the pencil beam scanning technique to tumors located close to the minimum range. The secondary neutrons are produced in the beam path including within the patient's body as a result of nuclear interactions. Therefore, unintended side effects may possibly occur. The research related to the secondary neutrons generated during proton therapy has been presented in a variety of studies worldwide, since 2007. In this study, we measured the magnitude of the secondary neutron dose depending on the location of the detector and the use of a range shifter at the beam nozzle of the proton scanning mode, which was recently installed. In addition, the production of secondary neutrons was measured and estimated as a function of the distance between the isocenter and detector. The neutron dose was measured using WENDI-II (Wide Energy Neutron Detection Instruments) and a Plastic Water phantom; a Zebra dosimeter and 4-cm-thick range shifter were also employed as a phantom. In conclusion, we need to consider the secondary neutron dose at proton scanning facilities to employ the range shifter reasonably and effectively.
  • Original Article 2016-09-30 2016-09-30 \ 0 \ 367 \ 128

    Treatment Plan Delivery Accuracy of the ViewRay System in Two-Headed Mode

    Jong Min Park, So-Yeon Park, Hong-Gyun Wu║, Jung-in Kim

    Abstract
    The aim of this study is to investigate the delivery accuracy of intensity-modulated radiation therapy (IMRT) plans in the two-headed mode of the ViewRayTM system in comparison with that of the normal operation treatment plan of the machine. For this study, a total of eight IMRT plans and corresponding verification plans were generated (four head and neck, two liver, and two prostate IMRT plans). The delivered dose distributions were measured using ArcCHECKTM with the insertion of an ionization chamber. We measured the delivered dose distributions in three-headed mode (normal operation of the machine), two-headed mode with head 1 disabled, two-headed mode with head 2 disabled, and two-headed mode with head 3 disabled. Therefore, a total of four measurements were performed for each IMRT plan. The global gamma passing rates (3%/3 mm) in three-headed mode, head 1 disabled, head 2 disabled, and head 3 disabled were 99.9±0.1%, 99.8±0.3%, 99.6±0.7%, and 99.7±0.4%, respectively. The difference in the gamma passing rates of the three- and two-headed modes was insignificant. With 2%/2 mm, the rates were 96.6±3.6%, 97.2±3.5%, 95.7±6.2%, and 95.5±4.3%, respectively. Between three-headed mode and head 3 disabled, a statistically significant difference was observed with a p-value of 0.02; however, the difference was minimal (1.1%). The chamber readings showed differences of approximately 1% between three- and two-headed modes, which were minimal. Therefore, the treatment plan delivery in the two-headed mode of the ViewRayTM system seems accurate and robust.
Korean Society of Medical Physics

Vol.35 No.2
2016-09-30

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

Current Issue   |   Archives

Most Keyword ?

What is Most Keyword?

  • It is most registrated keyword in articles at this journal during for 2 years.

Archives