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  • Review Article 2013-12-30 2013-12-30 \ 0 \ 292 \ 127

    Practical Considerations in Preparing an Institutional Procedure of Image Guided Radiation Therapy

    Byong Yong Yi

    Abstract
    Recent developments of image guided radiation therapy (IGRT), especially the On Board Imaging (OBI) system and the cone beam CT (CBCT), enable the radiation treatment more accurate and reliable. IGRT is widely used in the radiation therapy as a standard of care. Use of IGRT is even expected to increase in the near future. IGRT is only beneficial to patients when it is used with proper considerations of safety and appropriateness of the techniques. Institutional procedure should be developed based on the clinical need and the deep understanding of the system before applying the new technique to the clinic. Comprehensive QA program should be established before to the clinic and imaging dose should be considered when preparing the departmental practice guidelines for IGRT.
  • Review Article 2013-12-30 2013-12-30 \ 0 \ 209 \ 141

    Review on the Pre-treatment Quality Assurance for Intensity Modulated Radiation Therapy

    Youngyih Han

    This review paper deals with the current statues of pre-treatment quality assurance conducted for Intensity modulated radiation therapy. Focusing on the issues relevant to two-dimensional verification of absorbed dose distribution, review was made for the papers published during the last 3∼4 years. Lastly, the future development direction was projected.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 275 \ 68

    Visibility of Internal Target Volume of Dynamic Tumors in Free-breathing Cone-beam Computed Tomography for Image Guided Radiation Therapy

    Kevin I. Kauweloa, Justin C. Park, Ajay Sandhu, Todd Pawlicki, Bongyong Song, William Y. Song

    Abstract
    Respiratory-induced dynamic tumors render free-breathing cone-beam computed tomography (FBCBCT) images with motion artifacts complicating the task of quantifying the internal target volume (ITV). The purpose of this paper is to study the visibility of the revealed ITV when the imaging dose parameters, such as the kVp and mAs, are varied. The TrilogyTM linear accelerator with an On-Board Imaging (OBITM) system was used to acquire low-imaging-dose-mode (LIDM: 110 kVp, 20 mA, 20 ms/frame) and high-imaging-dose-mode (HIDM: 125 kVp, 80 mA, 25 ms/frame) FBCBCT images of a 3-cm diameter sphere (density=0.855 g/cm3) moving in accordance to various sinusoidal breathing patterns, each with an unique inhalation-to-exhalation (I/E) ratio, amplitude, and period. In terms of image ITV contrast, there was a small overall average change of the ITV contrast when going from HIDM to LIDM of 6.5±5.1% for all breathing patterns. As for the ITV visible volume measurements, there was an insignificant difference between the ITV of both the LIDM- and HIDM-FBCBCT images with an average difference of 0.5±0.5%, for all cases, despite the large difference in the imaging dose (approximately five-fold difference of ~0.8 and 4 cGy/scan). That indicates that the ITV visibility is not very sensitive to changes in imaging dose. However, both of the FBCBCT consistently underestimated the true ITV dimensions by up to 34.8% irrespective of the imaging dose mode due to significant motion artifacts, and thus, this imaging technique is not adequate to accurately visualize the ITV for image guidance. Due to the insignificant impact of imaging dose on ITV visibility, a plausible, alternative strategy would be to acquire more X-ray projections at the LIDM setting to allow 4DCBCT imaging to better define the ITV, and at the same time, maintain a reasonable imaging dose, i.e., comparable to a single HIDM-FBCBCT scan.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 390 \ 213

    A Smart Setup for Craniospinal Irradiation

    Jennifer L. Peterson, Laura A. Vallow, Siyong Kim, Henry E. Casale, Katherine S. Tzou

    Abstract
    Our purpose is to present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match, field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. To achieve this purpose, computed tomography simulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranial fields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the same source-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenter was placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for the lower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinal field. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the match line over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimization technique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. This supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dose modulation provides a simple and safe way to deliver treatment while minimizing dose inhomogeneity.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 250 \ 106

    The Feasibility Study of MRI-based Radiotherapy Treatment Planning Using Look Up Table

    Shin-Wook Kim*, Hun-Joo Shin*, Young-Kyu Lee, Jae-Hyuk Seo, Gi-Woong Lee,
    Hyeong-Wook Park, Jae-Choon Lee, Ae-Ran Kim, Ji-Na Kim, Myong-Ho Kim*,
    Chul-Seung Kay*, Hong-Seok Jang, Young-Nam Kang

    Abstract
    In the intracranial regions, an accurate delineation of the target volume has been difficult with only the CT data due to poor soft tissue contrast of CT images. Therefore, the magnetic resonance images (MRI) for the delineation of the target volumes were widely used. To calculate dose distributions with MRI-based RTP, the electron density (ED) mapping concept from the diagnostic CT images and the pseudo CT concept from the MRI were introduced. In this study, the look up table (LUT) from the fifteen patients’ diagnostic brain MRI images was created to verify the feasibility of MRI-based RTP. The dose distributions from the MRI-based calculations were compared to the original CT-based calculation. One MRI set has ED information from LUT (lMRI). Another set was generated with voxel values assigned with a homogeneous density of water (wMRI). A simple plan with a single anterior 6MV one portal was applied to the CT, lMRI, and wMRI. Depending on the patient’s target geometry for the 3D conformal plan, 6MV photon beams and from two to five gantry portals were used. The differences of the dose distribution and DVH between the lMRI based and CT-based plan were smaller than the wMRI-based plan. The dose difference of wMRI vs. lMRI was measured as 91 cGy vs. 57 cGy at maximum dose, 74 cGt vs. 42 cGy at mean dose, and 94 cGy vs. 53 at minimum dose. The differences of maximum dose, minimum dose, and mean dose of the wMRI-based plan were lower than the lMRI-based plan, because the air cavity was not calculated in the wMRI-based plan. These results prove the feasibility of the lMRI-based planning for brain tumor radiation therapy.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 219 \ 130

    Analysis of Acquisition Parameters That Caused Artifacts in Four-dimensional (4D) CT Images of Targets Undergoing Regular Motion

    Heesoon Sheen, Youngyih Han, Eunhyuk Shin

    Abstract
    The aim of this study was to clarify the impacts of acquisition parameters on artifacts in four-dimensional computed tomography (4D CT) images, such as the partial volume effect (PVE), partial projection effect (PPE), and mis-matching of initial motion phases between adjacent beds (MMimph) in cine mode scanning. A thoracic phantom and two cylindrical phantoms (2 cm diameter and heights of 0.5 cm for No.1 and 10 cm for No.2) were scanned using 4D CT. For the thoracic phantom, acquisition was started automatically in the first scan with 5 sec and 8 sec of gantry rotation, thereby allowing a different phase at the initial projection of each bed. In the second scan, the initial projection at each bed was manually synchronized with the inhalation phase to minimize the MMimph. The third scan was intentionally un-synchronized with the inhalation phase. In the cylindrical phantom scan, one bed (2 cm) and three beds (6 cm) were used for 2 and 6 sec motion periods. Measured target volume to true volume ratios (MsTrueV) were computed. The relationships among MMimph, MsTrueV, and velocity were investigated. In the thoracic phantom, shorter gantry rotation provided more precise volume and was highly correlated with velocity when MMimph was minimal. MMimph reduced the correlation. For moving cylinder No. 1, MsTrueV was correlated with velocity, but the larger MMimph for 2 sec of motion removed the correlation. The volume of No. 2 was similar to the static volume due to the small PVE, PPE, and MMimph. Smaller target velocity and faster gantry rotation resulted in a more accurate volume description. The MMimph was the main parameter weakening the correlation between MsTrueV and velocity. Without reducing the MMimph, controlling target velocity and gantry rotation will not guarantee accurate image presentation given current 4D CT technology.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 300 \ 69

    The Comparative Analysis of External Dose Reconstruction in EPID and Internal Dose Measurement Using Monte Carlo Simulation

    Joo-Young Jung, Do-Kun Yoon, Tae-Suk Suh

    Abstract
    The purpose of this study is to evaluate and analyze the relationship between the external radiation dose reconstruction which is transmitted from the patient who receives radiation treatment through electronic portal imaging device (EPID) and the internal dose derived from the Monte Carlo simulation. As a comparative analysis of the two cases, it is performed to provide a basic indicator for similar studies. The geometric information of the experiment and that of the radiation source were entered into Monte Carlo n-particle (MCNPX) which is the computer simulation tool and to derive the EPID images, a tally card in MCNPX was used for visualizing and the imaging of the dose information. We set to source to surface distance (SSD) 100 cm for internal measurement and EPID. And the water phantom was set to be 100 cm of the source to surface distance (SSD) for the internal measurement and EPID was set to 90 cm of SSD which is 10 cm below. The internal dose was collected from the water phantom by using mesh tally function in MCNPX, accumulated dose data was acquired by four-portal beam exposures. At the same time, after getting the dose which had been passed through water phantom, dose reconstruction was performed using back-projection method. In order to analyze about two cases, we compared the penetrated dose by calibration of itself with the absorbed one. We also evaluated the reconstructed dose using EPID and partially accumulated (overlapped) dose in water phantom by four-portal beam exposures. The sum dose data of two cases were calculated as each 3.4580 MeV/g (absorbed dose in water) and 3.4354 MeV/g (EPID reconstruction). The result of sum dose match from two cases shows good agreement with 0.6536% dose error.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 199 \ 157

    Development of DICOM Convert Program for the Geant4 Monte Carlo Simulation of the Radiotherapy

    Jeongku Kang, Dong Joon Lee

    Abstract
    The DICOM converter program of the Geant4 Monte Carlo simulation code for the application of radiotherapy was developed. We analysis the header part of the DICOM file and find various parameters, such as matrix size, pixel size, stored data bits, high bit, and padding values. Especially we evaluate every pixel value of the DICOM files. To conform the exact convert of the pixel values, we developed the verify program. As a result, the DICOM formats generated from difference CT vendors can be converted and verified for Genat4 calculations.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 280 \ 85

    Differences in Target Volume Delineation Using Typical Radiosurgery Planning System

    Su Chul Han, Dong Joon Lee

    Abstract
    Correct target volume delineation is an important part of radiosurgery treatment planning process. We designed head phantom and performed target delineation to evaluate the volume differences due to radiosurgery treatment planning systems and image acquisition system, CT/MR. Delineated mean target volume from CT scan images was 2.23±0.08 cm3 on BrainSCAN (NOVALS), 2.13±0.07 cm3 on Leksell gamma plan (Gamma Knife) and 2.24±0.10 cm3 on Multi plan (Cyber Knife). For MR images, 2.08±0.06 cm3 on BrainSCAN, 1.94±0.05 cm3 on Leksell gamma plan and 2.15±0.06 cm3 on Multi plan. As a result, Differences of delineated mean target volume due to radiotherapy planning system was 3% to 6%. And overall mean target volume from CT scan images was 6.36% larger than those of MR scan images.
  • Original Article 2013-12-30 2013-12-30 \ 0 \ 315 \ 126

    Convolution-Superposition Based IMRT Plan Study for the PTV Containing the Air Region: A Prostate Cancer Case

    Sei-Kwon Kang, Jai-Woong Yoon, Soah Park, Taejin Hwang, Kwang-Ho Cheong, Taejin Han, Haeyoung Kim, Me-Yeon Lee, Kyoung Ju Kim, Hoonsik Bae

    Abstract
    In prostate IMRT planning, the planning target volume (PTV), extended from a clinical target volume (CTV), often contains an overlap air volume from the rectum, which poses a problem inoptimization and prescription. This study was aimed to establish a planning method for such a case. There can be three options in which volume should be considered the target during optimization process; PTV including the air volume of air density (‘airOpt’), PTV including the air volume of density value one, mimicking the tissue material (‘density1Opt’), and PTV excluding the air volume (‘noAirOpt’). Using 10 MV photon beams, seven field IMRT plans for each target were created with the same parameter condition. For these three cases, DVHs for the PTV, bladder and the rectum were compared. Also, the dose coverage for the CTV and the shifted CTV were evaluated in which the shifted CTV was a copied and translated virtual CTV toward the rectum inside the PTV, thus occupying the initial position of the overlap air volume, simulating the worst condition for the dose coverage in the target. Among the three options, only density1Opt plan gave clinically acceptable result in terms of target coverage and maximum dose. The airOpt plan gave exceedingly higher dose and excessive dose coverage for the target volume whereas noAirOpt plan gave underdose for the shifted CTV. Therefore, for prostate IMRT plan, having an air region in the PTV, density modification of the included air to the value of one, is suggested, prior to optimization and prescription for the PTV. This idea can be equally applied to any cases including the head and neck cancer with the PTV having the overlapped air region. Further study is being under process.
Korean Society of Medical Physics

Vol.35 No.2
2013-12-30

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

Frequency: Quarterly

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