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  • Original Article 2008-03-25 2008-03-25 \ 0 \ 604 \ 1995

    99mTc Generator Safety Simulation Based on GEANT4

    Sang-Koo Kang, Dong-Hyun Han, Chong-Yeal Kim

    Abstract
    .Technisium (99mTc) is one of the most widely used radioactive isotopes for diagnosis in nuclear medicine. In general, technisium is produced inside the so called 99mTc generator which is usually made out of lead to shield relatively high energy radiation from 99Mo and its daughter nuclide 99mTc. In this paper, a GEANT4 simulation is carried out to test the safety of the 99mTc generator, taking the Daiichi product with radioactivity of 500 mCi as an example. According to the domestic regulation on radiation safety, the dose at 10 cm and 100 cm away from the surface of shielding container should not exceed 2.0 mSv/h and 0.02 mSv/h, respectively. The simulated dose turned out to be less than the limit, satisfying the domestic regulation.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 223 \ 483

    Comparison of Skin Dose Measurement Using Glass Dosimeter and Diode for Breast Cancer Patients

    Young Eun Ko*, Sung Ho Park, Byoung Joon Choi*, Hee-Sun Kim, Young Ju Noh*

    Abstract
    The purpose of this study was to measure the skin dose using the glass dosimeter and diode and to compare those measurements to the planned skin dose from the treatment planning system. For the reproducibility of the glass dosimeter (ASAHI TECHNO GLASS CIRPORATION, Japan), the same dose was irradiated to 40 glass dosimeters three times, among which 28 with the reproducibility within 3% were selected for the use of this study. For each of 27 breast cancer patients, the glass dosimeters and diodes were attached to 4 different locations on the skin to measure the dose during treatment. All the patients received one fraction of 180 cGy each. The maximum difference of measurements between the glass dosimeter and diode at the same location was 3.2%. Comparing with the planned skin dose from the treatment planning system (Eclipse v6.5, Varian, USA), the dose measured by the glass dosimeter and the diodeshowed on an average 3.4% and 2.3% difference, respectively. The measured doses were always less than the planned skin dose. This may be due to the specific errors of both detectors. Also, the difference may be caused by the fact that since the skin where the detectors were attached is pretty moveable, it was not fix the detectors on the skin.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 137 \ 453

    Evaluation of Difference between Skin Motion and Tumor Motion for Respiration Gated Radiotherapy

    Kyung Tae Kwon*, Sangwook Lim, Sung Ho Park*, Soo Il Kwon, Sung Soo Shin*, Sang‐wook Lee*, Seung Do Ahn*, Jong Hoon Kim*, Eun Kyung Choi*

    Abstract
    Accounting for tumor motion in treatment planning and delivery is one of the most recent and significant challenges facing radiotherapy. The purpose of this study was to investigate the correlation and clarified the relationship between the motion of an external marker using the Real‐Time Position Management (RPM) System and an internal organ motion signal obtained fluoroscope. We enrolled 10 patients with locally advanced lung cancer and liver cancer, retrospectively. The external marker was a plastic box, which is part of the RPM used to track the patient's respiration. We investigated the quantitatively correlation between the motions of an external marker with RPM and internal motion with fluoroscope. The internal fiducial motion is predominant in the caraniocaudal direction, with a range of 1.3∼3.5 cm with fluoroscopic unit. The external fiducial motion is predominant in the caraniocaudal direction, with a range of 0.43∼2.19 cm with RPM gating. The two measurements ratio is from 1.31 to 5.56. When the regularization guided standard deviation is from 0.08 to 0.87, mean 0.204 cm, except only for patients #3 separated by a mean 0.13 cm, maximum of 0.23 cm. This result is a good correlation between internal tumor motion imaged by fluoroscopic unit and external marker motion with RPM during expiration within 0.23 cm. We have demonstrated that gating may be best performed but special attention should be paid to gating for patients whose fiducials do not move in synchrony, because targeting on the correct phase difference alone would not guarantee that the entire tumor volume is within the treatment field.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 186 \ 267

    Verification of the PMCEPT Monte Carlo dose Calculation Code for Simulations in Medical Physics

    Oyeon Kum

    Abstract
    The parallel Monte Carlo electron and photon transport (PMCEPT) code [Kum and Lee, J. Korean Phys. Soc. 47, 716 (2006)] for calculating electron and photon beam doses has been developed based on the three dimensional geometry defined by computed tomography (CT) images and implemented on the Beowulf PC cluster. Understanding the limitations of Monte Carlo codes is useful in order to avoid systematic errors in simulations and to suggest further improvement of the codes. We evaluated the PMCEPT code by comparing its normalized depth doses for electron and photon beams with those of MCNP5, EGS4, DPM, and GEANT4 codes, and with measurements. The PMCEPT results agreed well with others in homogeneous and heterogeneous media within an error of 1∼3% of the dose maximum. The computing time benchmark has also been performed for two cases, showing that the PMCEPT code was approximately twenty times faster than the MCNP5 for 20-MeV electron beams irradiated on the water phantom. For the 18-MV photon beams irradiated on the water phantom, the PMCEPT was three times faster than the GEANT4. Thus, the results suggest that the PMCEPT code is indeed appropriate for both fast and accurate simulations.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 228 \ 420

    Image Based Quality Assurance of Range Compensator for Proton Beam Therapy

    Jin-Sung Kim, Myonggeun Yoon, Dongwook Kim, Young Kyung Lim, Jungwon Kwak, Soah Park, Dong Ho Shin, Jungwook Shin, Se Byeong Lee, Sung Yong Park, Kwan Ho Cho

    Abstract
    The main benefit of proton therapy over photon beam radiotherapy is the absence of exit dose, which offers the opportunity for highly conformal dose distributions to target volume while simultaneously irradiating less normal tissue. For proton beam therapy two patient specific beam modifying devices are used. The aperture is used to shape the transverse extension of the proton beam to the shape of the tumor target and a patient-specific compensator attached to the block aperture when required and used to modify the beam range as required by the treatment plan for the patient. A block of range shifting material, shaped on one face in such a way that the distal end of the proton field in the patient takes the shape of the distal end of the target volume. The mechanical quality assurance of range compensator is an essential procedure to confirm the 3 dimensional patient-specific dose distributions. We proposed a new quality assurance method for range compensator based on image processing using X-ray tube of proton therapy treatment room. The depth information, boundaries of each depth of plan compensatorfile and x-ray image of compensator were analyzed and presented over 80% matching results with proposed QA program.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 258 \ 1231

    Wireless Energy and Data Transmission Using Inductive Coupling

    Joon Ha Lee

    Abstract
    Bio-implantable devices such as heart pacers, gastric pacers and drug-delivery systems require power for carrying out their intended functions. These devices are usually powered through a battery implanted with the system or are wired to an external power source. This paper describes an inductive power transmission link, which was developed for an implantable stimulator for direct stimulation of denervated muscles. The carrier frequency is around 1 MHz, the transmitter coil has a diameter of 46 mm, and the implant coil is 46 mm. Data transmission to the implant with amplitude shift keying (ASK) and back to the transmitter with passive telemetry can be added without major design changes. We chose the range of coil spacing (2 to 30 mm) to care for lateral misalignment, as it occurs in practical use. If the transmitter coil has a well defined and reliable position in respect to the implant, a smaller working range might be sufficient. Under these conditions the link can be operated in fixed frequency mode, and reaches even higher efficiencies of up to 37%. The link transmits a current of 50 mA over a distance range of 2-15 mm with an efficiency of more than 20% in tracking frequency. The efficiency of the link was optimized with different approaches. A class E transmitter was used to minimize losses of the power stage. The geometry and material of the transmitter coil was optimized for maximum coupling. Phase lock techniques were used to achieve frequency tracking, keeping the transmitter optimally tuned at different coupling conditions caused by coil distance variations.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 364 \ 510

    Comparison of Radiation Dose in the Measurement of MDCT Radiation Dose according to Correction of Temperatures and Pressure, and Calibration of Ionization Chamber

    Chang-Lae Lee*, Hee-Joung Kim*, Seong Su Jeon, Hyo-Min Cho*, Sora Nam, Ji-Young Jung*, Young-Jin Lee*, Seung-Jae Lee*, Kyung-Rae Dong

    Abstract
    This study aims to conduct the comparative analysis of the radiation dose according to before and after the calibration of the ionization chamber used for measuring radiation dose in the MDCT, as well as of CTDIW according to temperature and pressure correction factors in the CT room. A comparative analysis was conducted based on the measured MDCT (GE light speed plus 4 slice, USA) data using head and body CT dosimetric phantom, and Model 2026C electrometer (RADICAL 2026C, USA) calibrated on March 21, 2007. As a result, the CTDIW value which reflected calibration factors, as well as correction factors of temperature and pressure, was found to be the range of 0.479~3.162 mGy in effective radiation dose than the uncorrected values. Also, under the routine abdomen routine CT image acquisition conditions used in reference hospitals, patient effective dose was measured to indicate the difference of the maximum of 0.7 mSv between before and after the application of such factors. These results imply that the calibration of the ion chamber, and the correction of temperature and pressure of the CT room are crucial in measuring and calculating patient effective dose. Thus, to measure patient radiation dose accurately, the detailed information should be made available regarding not only the temperature and pressure of the CT room, but also the humidity and recombination factor, characteristics of X-ray beam quality, exposure conditions, scan region, and so forth.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 248 \ 322

    Study on the Dose Characteristics of the PTW-LinaCheck Dosimeter and Its Application to Daily Output Measurement

    Dong Hyeok Jeong*, Kang Kyoo Lee*, Un Chul Moon*, Hyun Jin Kim*, Young Seok Kim*, Sun Rock Moon*

    Abstract
    In this study, we have investigated the dose characteristics of PTW-LinaCheck designed to detect output of medical LINAC and discussed clinical use of the detector. The reproducibility, linearity, and dose rate dependency of the dosimeter were measured for photons of 6 and 15 MV and the electrons of 4, 6, 9, 12, and 16 MeV. To know the error ranges of the measured data in daily output measurement, the response variations due to geometrical setup errors were measured. As a result of measurement, the error range from the geometrical setup and the reproducibility was less than ±0.6% for given beam qualities in daily output measurement, where the errors from the linearity and the dose rate dependency were negligible. Finally, we concluded that the LinaCheck dosimeter has a good characteristics in terms of dose and setup convenience in daily output measurement. In addition we have shown an examples of clinical use of this dosimeter for measuring daily output more than 60 days.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 1295 \ 2923

    Imaging Characteristics of Computed Radiography Systems

    Jiyoung Jung*, Hye-Suk Park*, Hyo-Min Cho*, Chang-Lae Lee*,Sora Nam, Young-Jin Lee*, Hee-Joung Kim*

    Abstract
    With recent advancement of the medical imaging systems and picture archiving and communication system (PACS), installation of digital radiography has been accelerated over past few years. Moreover, Computed Radiography (CR) which was well established for the foundation of digital x-ray imaging systems at low cost was widely used for clinical applications. This study analyzes imaging characteristics for two systems with different pixel sizes through the Modulation Transfer Function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE). In addition, influence of radiation dose to the imaging characteristics was also measured by quantitative assessment. A standard beam quality RQA5 based on an international electro-technical commission (IEC) standard was used to perform the x-ray imaging studies. For the results, the spatial resolution based on MTF at 10% for Agfa CR system with I.P size of 8X10 inches and 14×17 inches was measured as 3.9 cycles/mm and 2.8 cycles/mm, respectively. The spatial resolution based on MTF at 10% for Fuji CR system with I.P size of 8X10 inches and 14×17 inches was measured as 3.4 cycles/mm and 3.2 cycles/mm, respectively. There was difference in the spatial resolution for 14×17 inches, although radiation dose does not effect to the MTF. The NPS of the Agfa CR system shows similar results for different pixel size between 100 Ռm for 8×10 inch I.P and 150 Ռm for 14×17 inch I.P. For both systems, the results show better NPS for increased radiation dose due to increasing number of photons. DQE of the Agfa CR system for 8X10 inch I.P and 14×17 inch I.P resulted in 11% and 8.8% at 1.5 cycles/mm, respectively. Both systems show that the higher level of radiation dose would lead to the worse DQE efficiency. Measuring DQE for multiple factors of imaging characteristics plays very important role in determining efficiency of equipment and reducing radiation dose for the patients. In conclusion, the results of this study could be used as a baseline to optimize imaging systems and their imaging characteristics by measuring MTF, NPS, and DQE for different level of radiation dose.
  • Original Article 2008-03-25 2008-03-25 \ 0 \ 201 \ 211

    Electrical Stimulation Parameters in Normal and Degenerate Rabbit Retina

    Gye-Hwan Jin*, Yong Sook Goo

    Abstract
    Retinal prosthesis is regarded as the most feasible method for the blind caused by retinal diseases such as retinitis pigmentosa (RP) or age related macular degeneration (AMD). Recently Korean consortium launched for developing retinal prosthesis. One of the prerequisites for the success of retinal prosthesis is the optimization of the electrical stimuli applied through the prosthesis. Since electrical characteristics of degenerate retina are expected to differ from those of normal retina, we performed voltage stimulation experiment both in normal and degenerate retina to provide a guideline for the optimization of electrical stimulation for the upcoming prosthesis. After isolation of retina, retinal patch was attached with the ganglion cell side facing the surface of microelectrode arrays (MEA). 8×8 grid layout MEA (electrode diameter: 30Ռm, electrode spacing: 200Ռm, and impedance: 50 kԹ at 1 kHz) was used to record in-vitro retinal ganglion cell activity. Mono-polar electrical stimulation was applied through one of the 60 MEA channel, and the remaining channels were used for recording. The electrical stimulus was a constant voltage, charge-balanced biphasic, anodic-first square wave pulse without interphase delay, and 50 trains of pulse was applied with a period of 2 sec. Different electrical stimuli were applied. First, pulse amplitude was varied (voltage: 0.5∼3.0 V). Second, pulse duration was varied (100∼1,200Ռs). Evoked responses were analyzed by PSTH from averaged data with 50 trials. Charge density was calculated with Ohm's and Coulomb's law. In normal retina, by varying the pulse amplitude from 0.5 to 3 V with fixed duration of 500 Ռs, the threshold level for reliable ganglion cell response was found at 1.5 V. The calculated threshold of charge density was 2.123 mC/cm2. By varying the pulse duration from 100 to 1,200Ռs with fixed amplitude of 2 V, the threshold level was found at 300Ռs. The calculated threhold of charge density was 1.698 mC/cm2. Even after the block of ON-pathway with L-(1)-2-amino-4-phosphonobutyric acid (APB), electrical stimulus evoked ganglion cell activities. In this APB-induced degenerate retina, by varying the pulse duration from 100 to 1200 Ռs with fixed voltage of 2 V, the threshold level was found at 300Ռs, which is the same with normal retina. More experiment with APB-induced degenerate retina is needed to make a clear comparison of threshold of charge density between normal and degenerate retina.
Korean Society of Medical Physics

Vol.35 No.2
2008-03-25

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

Frequency: Quarterly

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