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  • Original Article 2010-12-25 2010-12-25 \ 0 \ 260 \ 170

    Evaluation of the Secondary Particle Effect in Inhomogeneous Media for Proton Therapy Using Geant4 Based MC Simulation

    So-Hyun Park*, Won-Gyun Jung*, Jeong-Eun Rah, Sungyong Park, Tae-Suk Suh*

    Abstract
    In proton therapy, the analysis of secondary particles is important due to delivered dose outside the target volume and thus increased potential risk for the development of secondary cancer. The purpose of this study is to analyze the influence of secondary particles from proton beams on fluence and energy deposition in the presence of inhomogeneous material by using Geant4 simulation toolkit. The inhomogeneity was modeled with the condition that the adipose tissue, bone and lung equivalent slab with thickness of 2 cm were inserted at 30% (Plateau region) and 80% (Bragg peak region) dose points of maximum dose in Bragg curve. The energy of proton was varied with 100, 130, 160 and 190 MeV for energy dependency. The results for secondary particles were presented for the fluence and deposited energy of secondary particles at inhomogeneous condition. Our study demonstrates that the fluence of secondary particles is neither influenced insertion of inhomogeneties nor the energy of initial proton, while there is a little effect by material density. The deposited energy of secondary particles has a difference in the position placed inhomogeneous materials. In the Plateau region, deposited energy of secondary particles mostly depends on the density of inserted materials. Deposited energy in the Bragg region, in otherwise, is influenced by both density of inserted material and initial energy of proton beams. Our results suggest a possibility of prediction about the distribution of secondary particles within complex heterogeneity.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 172 \ 292

    nalysis on the Effect of Field Width in the Delineation of Planning Target Volume for TomoTherapy

    Ju-Young Song, Byung-Sik Nah, Woong-Ki Chung, Sung-Ja Ahn, Taek-Keun Nam, Mee-Sun Yoon, Jae-Uk Jung

    Abstract
    The Hi-Art system for TomoTherapy allows only three (1.0 cm, 2.5 cm, 5.0 cm) field widths and this can produce different dose distribution around the end of PTV (Planning target volume) in the direction of jaw movement. In this study, we investigated the effect of field width on the dose difference around the PTV using DQA (Delivery quality assurance) phantom and real clinical patient cases. In the analysis with DQA phantom, the calculated dose and irradiated films showed that the more dose was widely spreaded out in the end region of PTV as increase of field width. The 2.5 cm field width showed a 1.6 cm wider dose profile and the 5.0 cm field width showed a 4.2 cm wider dose profile compared with the 1.0 cm field width in the region of 50% of maximum dose. The analysis with four patient cases also showed the similar results with the DQA phantom which means that more dose was irradiated around the superior and inferior end of PTV as an increase of field width. The 5.0 cm field width produced the remarkable high dose distribution around the end region of PTV and we could evaluate the effect quantitatively with the calculation of DVH (Dose volume histogram) of the virtual PTVs which were delineated around the end of PTV in the direction of jaw variation. From these results, we could verify that the margin for PTV in the direction of table movement should be reduced compared with the conventional margin for PTV when the large field such as 5.0 cm was used in TomoTherapy.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 143 \ 301

    Error Analysis of Delivered Dose Reconstruction Using Cone-beam CT and MLC Log Data

    Kwang-Ho Cheong, Soah Park, Sei-Kwon Kang, Tae-Jin Hwang, Me Yeon Lee, Kyoung-Joo Kim, Hoonsik Bae, Do-Hoon Oh

    Abstract
    We aimed to setup an adaptive radiation therapy platform using cone-beam CT (CBCT) and multileaf collimator (MLC) log data and also intended to analyze a trend of dose calculation errors during the procedure based on a phantom study. We took CT and CBCT images of Catphan-600 (The Phantom Laboratory, USA) phantom, and made a simple step-and-shoot intensity-modulated radiation therapy (IMRT) plan based on the CT. Original plan doses were recalculated based on the CT (CTplan) and the CBCT (CBCTplan). Delivered monitor unit weights and leaves-positions during beam delivery for each MLC segment were extracted from the MLC log data then we reconstructed delivered doses based on the CT (CTrecon) and CBCT (CBCTrecon) respectively using the extracted information. Dose calculation errors were evaluated by two-dimensional dose discrepancies (CTplan was the benchmark), gamma index and dose-volume histograms (DVHs). From the dose differences and DVHs, it was estimated that the delivered dose was slightly greater than the planned dose; however, it was insignificant. Gamma index result showed that dose calculation error on CBCT using planned or reconstructed data were relatively greater than CT based calculation. In addition, there were significant discrepancies on the edge of each beam while those were less than errors due to inconsistency of CT and CBCT. CBCTrecon showed coupled effects of above two kinds of errors; however, total error was decreased even though overall uncertainty for the evaluation of delivered dose on the CBCT was increased. Therefore, it is necessary to evaluate dose calculation errors separately as a setup error, dose calculation error due to CBCT image quality and reconstructed dose error which is actually what we want to know.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 202 \ 624

    A Method to Calculate a Pass Rate of the Ճ-index Analysis in Tomotherapy Delivery Quality Assurance (DQA)

    Dahl Park*, Yong Ho Kim*, Won Taek Kim, Dong Won Kim, Dong Hyun Kim*, Hosang Jeon, Ji Ho Nam, Sangwook Lim

    Abstract
    DQA, a patient specific quality assurance in tomotherapy, is usually performed using an ion chamber and a film. The result of DQA is analysed with the treatment planning system called Tomo Planning Station (TomoPS). The two-dimensional dose distribution of film measurement is compared with the dose distribution calculated by TomoPS using the Ճ-index analysis. In Ճ-index analysis, the criteria such as 3%/3 mm is used and we verify that whether the rate of number of points which pass the criteria (pass rate) is within tolerance. TomoPS does not provide any quantitative information regarding the pass rate. In this work, a method to get the pass rate of the Ճ-index analysis was suggested and a software PassRT which calculates the pass rate was developed. The results of patient specific QA of the intensity modulated radiation therapy measured with I'mRT MatriXX (IBA Dosimetry, Germany) and DQA of tomotherapy measured with film were used to verify the proposed method. The pass rate was calculated using PassRT and compared with the pass rate calculated by OmniPro I'mRT (IBA Dosimetry, Germany). The average difference between the two pass rates was 0.00% for the MatriXX measurement. The standard deviation and the maximum difference were 0.02% and 0.02%, respectively. For the film measurement, average difference, standard deviation and maximum difference were 0.00%, 0.02% and 0.02%, respectively. For regions of interest smaller than 24.3×16.6 cm2 the proposed method can be used to calculate the pass rate of the gamma index analysis to one decimal place and will be helpful for the more accurate DQA in tomotherapy.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 300 \ 705

    Imaging Studies in Mouse Brain Using Clinical 3T MRI Scanner

    Soo Mee Lim*, Eun-Mi Park

    Abstract
    The purpose of this study was to explore the potentials of a clinical 3T MRI in mouse brains and technical adaptation and optimization. T1-weighted images (T1WI), T2-weighted images (T2WI), FLAIR (Fluid Attenuated Inversion Recovery) images, Gadolinium enhanced T1-weighted images (Gd-T1WI), Diffusion weighted images (DWI) were acquired in brain of 2 mice (weight 20∼25 g) with cerebral infarction by occlusion of right middle cerebral artery, 1 hour, 24 hours, 72 hours after infarction and 1 normal mouse brain using clinical 3T MRI scanner. We analyzed differentiation of striatum, ventricle, cerebral cortex, and possibility of detection of acute cerebral infarction. We could differentiate the striatum, ventricle, cerebral cortex on T2WI and on DWI, FLAIR, T1WI, the differentiation of each anatomy of brain was not definite, but acute cerebral infarction was detected on DWI of 1 hour, 24 hours, 72 hours after infarction and on T2WI, FLAIR of 24 hours, 72 hours after infarction. Clinical 3T MRI can be used in differentiation of anatomy of mouse brains and DWI can be helpul in detection of acute cerebral infarction in acute phase. With technical adaptation and optimization clinical 3T MRI can be useful tool for provide preclinical and clinical small animal studies.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 102 \ 199

    The Dosimetric Effect on Real PTV and OARs at Various Image Fusion Protocol for Pituitary Adenomas

    Kyung-Nam Lee*, Dong-Joon Lee, Tae-Suk Suh*

    Abstract
    The purpose of this study is to verify the dosimetric effect on real PTV (planning target volume) coverage and safety of OARs (organs at risk) at various image fusion protocol-based radiosurgery plan for pituitary adenomas. Real PTV coverage and its variation was acquired and maximum dose and the volume absorbing above threshold dose were also measured for verifying the safety of optic pathway and brainstem. The protocol that can reduce superior-inferior uncertainty by using both axial and coronal MR (magnetic resonance) image sets shows relatively lower values than that of case using only axial image sets. As a result, the image fusion protocol with both axial and coronal image sets can be beneficial to generate OAR-weighted radiosurgery plan.
  • Original Article 2010-12-25 2010-12-25 \ 0 \ 206 \ 584

    Digital Tomosynthesis for Patient Alignment System Using Half-fan Mode CBCT Projection Images

    Justin C. Park, Sung Ho Park*, Jin Sung Kim, Youngyih Han, Sang-Gyu Ju, Eunhyuk Shin, Jung Suk Shin, Hee-Chul Park, Yong Chan Ahn, Willian Y. Song

    Abstract
    To generate on-board digital tomosynthesis (DTS) for three-dimensionalimage-guided radiation therapy (IGRT) as an alternative to conventional portal imaging or on-board cone-beam computed tomography (CBCT), two clinical cases (liver and bladder) were selected to illustrate the capabilities of on-board DTS for IGRT. DTS images were generated from subsets of CBCT projection data (45, 162 projections) using half-fan mode scanning with a Feldkamp-type reconstruction algorithm. Digital tomosynthesis slices appeared similar to coincident CBCT planes and yielded substantially more anatomic information. Improved bony and soft-tissue visibility in DTS images is likely to improve target localization compared with radiographic verification techniques and might allow for daily localization of a soft-tissue target. Digital tomosynthesis might allow targeting of the treatment volume on the basis of daily localization.
Korean Society of Medical Physics

Vol.35 No.2
2010-12-25

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

Frequency: Quarterly

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