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  • Original Article 2009-03-25 2009-03-25 \ 0 \ 390 \ 586

    Dose Comparison of Treatment Plans Using Different Ir-192 Sources and Treatment Planning Systems for Intracavitary HDR Brachytherapy

    Dong-Wook Park*, Young Seok Kim*, Sung Ho Park*, Eun Kyung Choi*, Jong Hoon Kim*, Sang-Wook Lee*, Si Yeol Song*, Seung Do Ahn*, Young Joo Noh

    Abstract
    For HDR intracavitary brachytherapy with ovoids and a tandem, we compared the dose discrepancy of treatment plans using two different Ir-192 sources (microSelectron, Varian) and generated on two different treatment planning systems (PLATO, BrachyVision). The treatment plans of ten patient treated from Oct. 2007 to Jan. 2008 were selected for these comparisons. For the comparison of dose calculation using different sources, the average discrepancies were -0.910.09%, -0.270.07%, 0.220.39%, and 0.880.37% in total treatment time and at B-point and ICRU bladder and rectum reference point, respectively. Comparing the two systems, the average dose discrepancies between treatment planning programs were -0.220.42%, -0.250.29%, -0.230.63%, and -0.170.76%, and the average dose discrepancies between positioning methods (PLATO with film and BrachyVision with digitial image) were -0.610.59%, -0.770.45%, -0.721.70%, and 0.352.82% at A-point, B-point, and ICRU bladder and rectum reference points, respectively. The rectal dose discrepancies between two systems were reached 5.87%. The difference in the dwell position expected by each TPS are mainly affected by the differences in the positioning method in TPSs and have an effect on dose calculations of rectal and bladder located in AP direction.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 374 \ 178

    Chamber to Chamber Variations of a Cylindrical Ionization Chamber for the Calibration of an 192Ir Brachytherapy Source Based on an Absorbed Dose to Water Standards

    Seong Hoon Kim*, Hyundo Huh, Sang Hyun Choi, Chan Hyeong Kim,Chul Hee Min, Dong Oh Shin, Jinho Choi

    Abstract
    This work is for the preliminary study for the calibration of an 192Ir brachytherapy source based on an absorbed dose to water standards. In order to calibrate brachytherapy sources based on absorbed dose to water standards using a clyndirical ionization chamber, the beam quality correction factor

    k _{Q,Q _{o}}

    is needed. In this study

    k _{Q,Q _{o}}

    s were determined by both Monte carlo simulation and semiexperimental methods because of the realistic difficulties to use primary standards to measure an absolute dose at a specified distance. The 5 different serial numbers of the PTW30013 chamber type were selected for this study. While chamber to chamber variations ran up to maximum 4.0% with the generic

    k _{Q,Q _{0}} ^{g e n}
    , the chamber to chamber variations were within a maximum deviation of 0.5% with the individual

    k _{Q,Q _{0}} ^{i n d}

    . The results show why and how important ionization chambers must be calibrated individually for the calibration of 192Ir brachytherapy sources based on absorbed dose to water standards. We hope that in the near future users will be able to calibrate the brachytherapy sources in terms of an absorbed dose to water, the quantity of interest in the treatment, instead of an air kerma strength just as the calibration in the high energy photon and electron beam.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 235 \ 238

    Analysis of Dose Distribution on Critical Organs for Radiosurgery with CyberKnife Real-Time Tumor Tracking System

    Hyun Do Huh*, Sang Hyoun Choi*, Woo Chul Kim*, Hun Jeong Kim*, Seong Hoon Kim, Young Hoon Ji, Kum Bae Kim, Sang Hoon Lee, Jinho Choi, Rena Lee, Dong Oh Shin

    Abstract
    We measured the dose distribution for spinal cord and tumor using Gafchromic film, applying 3D and 4D-Treatment Planning for lung tumor within the phantom. A measured dose distribution was compared with a calculated dose distribution generated from 3D radiation treatment planning and 4D radiation treatment planning system. The agreement of the dose distribution in tumor for 3D and 4D treatment planning was 90.6%, 97.64% using gamma index computed for a distance to agreement of 1 mm and a dose difference of 3%. However, a gamma agreement index of 3% dose difference tolerence of and 2 mm distance to agreement, the accordance of the dose distribution around cord for 3D and 4D radiation treatment planning was 57.13%, 90.4%. There are significant differences between a calculated dose and a measured dose for 3D radiation treatment planning, no significant differences for 4D treatment planning. The results provide the effectiveness of the 4D treatment planning as compared to 3D. We suggest that the 4-dimensional treatment planning should be considered in the case where such equipments as Cyberknife with the real time tracking system are used to treat the tumors in the moving organ.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 397 \ 2331

    Standardization of the Method of Measuring Average Glandular Dose (AGD) and Evaluation of the Breast Composition and Thickness for AGD

    Hye-Suk Park, Hee-Joung Kim, Chang-Lae Lee, Hyo-Min Cho, A-Ram Yu

    Abstract
    Breast cancer is the most common form of cancer among korean woman. Therefore, the early detection activities of breast cancer such as breast self-examinations, clinical breast examinations, mammography are important. A yearly mammography examination has been recommended for women aged 40 and older for the early detection of breast cancer in asymptomatic periods. However, the glandular tissue of breast is the most radiation-sensitive tissue, and the determination of average glandular dose (AGD) forms an important part of the quality control of the mammographic systems. Because of the difficulty of estimating AGD directly, it is often estimated from the measurements of the incident air kerma and by applying the appropriate conversion factors. The primary objective of this study was to standardize the method of measuring AGD. The secondary objective was to evaluate the relationships between AGD per various composition and thickness of the breast using Monte Carlo simulations. As a result, we standardized the method of measuring AGD according to International Atomic Energy Agency (IAEA) guidelines (CoP: an international code of practice). Overall, AGD for mammographic practice in Korea was less than 3.0 mGy recommended by the Korea Food and Drug Adminstration (KFDA) protocol, and Korean Institute for Accreditation of Medical Image (KIAMI). The measured and simulated AGD for a given condition were calculated as 1.7 and 1.6 mGy, respectively. For the AGDs obtained, there was no significant difference between them. The simulated AGD was dependent on the fraction of glandular tissue of the breast. The AGD increases with increasing of the breast glandularity due to increasing absorption of low energy photons. The AGD also increases as a function of breast thickness. In conclusion, the results of this study could be used as a baseline to establish a reference level of radiation dose in mammography.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 220 \ 543

    Quality Correction for Ir-192 Gamma Rays in Air Kerma Strength Dosimetry Using Cylindrical Ionization Chambers

    Dong Hyeok Jeong*, Jhin Kee Kim, Ki Hwan Kim, Young Kee Oh, Soo Kon Kim, Kang Kyoo Lee*, Sun Rock Moon*

    Abstract
    The quality correction in the air kerma dosimetry for Ir-192 using farmer type ionization chambers calibrated by Co-60 quality is required. In this study we determined quality factor (

    k_u
    ) of two ionization chambers of PTW-N30001 and N23333 for Ir-192 source using dosimetric method. The quality factors for energy spectrum of microSelectron were determined as

    k_u
    =1.016 and 1.017 for PTW-N30001 and N23333 ionization chambers respectively. We applied quality factors in air kerma dosimetry for microSelectron source and compared with reference values. As a results we found that the differences between reference air kerma rate and measured it with and without quality correction were about -0.5% and -2.0% respectively.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 259 \ 712

    A Study of Radiation Exposure in Proton Therapy Facility

    Sang Hoon Lee, Dongho Shin, Myonggeun Yoon, Jungwook Shin, Jeong-Eun Rah, Jungwon Kwak*, Sung Yong Park, Kyung Hwan Shin, Doo-Hyun Lee,Sung Hwan Ahn, Dae Yong Kim, Kwan Ho Cho, Se Byeong Lee

    Abstract
    Proton therapy facility, which is recently installed at National Cancer Center in Korea, generally produces a large amount of radiation near cyclotron due to the secondary particles and radioisotopes caused by collision between proton and nearby materials during the acceleration. Although the level of radiation by radioisotope decreases in length of time, radiation exposure problem still exists since workers are easily exposed by a low level of radiation for a long time due to their job assignment for maintenance or repair of the proton facility. In this paper, the working environment near cyclotron, where the highest radiation exposure is expected, was studied by measuring the degree of radiation and its duration for an appropriate level of protective action guide. To do this, we measured the radiation change in the graphite based energy degrader, the efficiency of transmitted beam and relative activation degree of the transmission beam line. The results showed that while the level of radiation exposure around cyclotron and beam line during the operation is much higher than the other radiation therapy facilities, the radiation exposure rate per year is under the limit recommended by the law showing 1∼3 mSv/year.
  • Original Article 2009-03-25 2009-03-25 \ 0 \ 336 \ 235

    Commissioning of a micro-MLC (mMLC) for Stereotactic Radiosurgery

    Dong Hyeok Jeong*, Kyo Chul Shin, Jeung Kee Kim, Soo Kon Kim, Sun Rock Moon*, Kang Kyoo Lee*

    Abstract
    The 4 bank mico-MLC (mMLC; Acculeaf, Direx, Isral) has been commissioned for clinical use of linac based stereotactic radiosurgery. The geometrical parameters to control the leaves were determined and comparisons between measured and calculated by the calculation model were performed in terms of absolute dose (cGy/100 MU). As a result of evaluating calculated dose for various field sizes and depths of 5 and 10 cm in water in the geometric condition of fixed SSD (source to surface distance) and fixed SCD (source to chamber distance), most of differences were within 1% for 6 MV and 15 MV x-rays. The penumbral widths at the isocenter were approximately evaluated to 0.29∼0.43 cm depending on the field size for 6 MV and 0.36∼0.51 cm for 15 MV x-rays. The average transmission and leakage for 6 MV and 15 MV x-rays were 6.6% and 7.4% respectively in single level of leaves fully closed. In case of dual level of leaves fully closed the measured transmission is approximately 0.5% for both 6 MV and 15 MV x-rays. Through the commissiong procedure we could verify the dose characteristics of mMLC and approximately evaluate the error ranges for treatment planning system.
Korean Society of Medical Physics

Vol.35 No.4
2009-03-25

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

Frequency: Quarterly

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