Review Article 2013-12-30 2013-12-30 0 381 137

방사선 치료용 영상 장치 지침서 작성을 위한 실용적인 고려사항

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

이병용

Byong Yong Yi

Abstract

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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 0 308 162

세기변조 방사선치료의 환자 치료 전 선량보증에 대한 고찰

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

한영이

Youngyih Han

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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 0 412 72

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

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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 Trilogy^TM linear accelerator with an On-Board Imaging (OBI^TM) 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 0 516 214

A Smart Setup for Craniospinal Irradiation

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

Abstract

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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 0 317 121

Look Up Table을 이용한 자기공명영상 기반 방사선 치료계획의 타당성 분석 연구

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

김신욱^*ㆍ신헌주^*ㆍ이영규^†ㆍ서재혁^‡ㆍ이기웅^§ㆍ박형욱^§ㆍ이재춘^§, 김애란^∥ㆍ김지나^∥ㆍ김명호^*ㆍ계철승*ㆍ장홍석^†ㆍ강영남^†

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

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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 0 291 162

표적이 규칙적으로 움직일 때 생기는 4DCT 영상의 모션 아티팩트(Motion Artifact) 관련된 원인분석

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

신희순^*†ㆍ한영이^*‡ㆍ신은혁^‡

Heesoon Sheen, Youngyih Han, Eunhyuk Shin

Abstract

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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 0 434 73

몬테 카를로 전산모사를 통한 EPID의 외부적 선량 재구성과 내부 선량 계측과의 비교 및 분석

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

정주영ㆍ윤도군ㆍ서태석

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

Abstract

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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 0 315 171

방사선치료의 Geant4 전산모사를 위한 DICOM 변환 프로그램 개발

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

강정구^*ㆍ이동준^†

Jeongku Kang, Dong Joon Lee

Abstract

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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 0 402 90

각각의 방사선수술 치료계획시스템에 따른 동일 병변의 체적 차이 비교

Differences in Target Volume Delineation Using Typical Radiosurgery Planning System

한수철^*†ㆍ이동준^‡

Su Chul Han, Dong Joon Lee

Abstract

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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 0 438 132

Convolution-Superposition 알고리즘을 이용한 치료계획시스템에서 공기가 포함된 표적체적에 대한 IMRT 플랜: 전립선 케이스

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

강세권ㆍ윤제웅ㆍ박소아ㆍ황태진ㆍ정광호ㆍ한태진ㆍ김해영ㆍ이미연ㆍ김경주ㆍ배훈식

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

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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.