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KMID : 1164220160280010077
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Journal of Korean Society for Radiotherapeutic Technology
2016 Volume.28 No. 1 p.77 ~ p.86
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The evaluation for the usability ofthe Varian Standard Couch modelingusing Treatment Planning System
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Song Yong-Min
Kim Jin-Man
Choi Ji-Min
Choi Byeong-Ki
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Abstract
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Purpose : When a radiation treatment, there is an attenuation by Carbon Fiber Couch. In this study, we tried to evaluate the usability of the Varian Standard Couch(VSC) by modeling with Treatment Planning System (TPS).
Materials and Methods : VSC was scanned by CBCT(Cone Beam Computed Tomography) of the Linac(Clinac IX, VARIAN, USA), following the three conditions of VSC, Side Rail OutGrid(SROG), Side Rail InGrid(SRIG), Side Rail In OutSpine Down Bar(SRIOS). After scan, the data was transferred to TPS and modeled by contouring Side Rail, Side Bar Upper, Side Bar Lower, Spine Down Bar automatically. We scanned the Cheese Phantom(Middelton, USA) using Computed Tomography(Light Speed RT 16, GE, USA) and transfer the data to TPS, and apply VSC modeled previously with TPS to it. Dose was measured at the isocenter of Ion Chamber(A1SL, Standard imaging, USA) in Cheese Phantom using 4 and 10 MV radiation for every 5°gantry angle in a different filed size(3X3cm², 10X10cm²) without any change of MU(=100), and then we compared the calculated dose and measured dose. Also we included dose at the 127°in SRIG to compare the attenuation by Side Bar Upper.
Results : The density of VSC by CBCT in TPS was 0.9g/cm³, and in the case of Spine Down Bar, it was 0.7g/cm³. The
radiation was attenuated by 17.49%, 16.49%, 8.54%, and 7.59% at the Side Rail, Side Bar Upper, Side Bar Lower, and Spine
Down Bar. For the accuracy of modeling, calculated dose and measured dose were compared. The average error was 1.13% and the maximum error was 1.98% at the 170°beam crossing the Spine Down Bar.
Conclusion : To evaluate the usability for the VSC modeled by TPS, the maximum error was 1.98% as a result of compassion between calculated dose and measured dose. We found out that VSC modeling helped expect the dose, so we think that it will be helpful for the more accurate treatment.
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KEYWORD
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Varian Standard Couch, Beam Attenuation, Model Based Segmentation
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