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KMID : 1164220210330010117
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Journal of Korean Society for Radiotherapeutic Technology
2021 Volume.33 No. 1 p.117 ~ p.125
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Evaluation of VMAT Dose Accuracy According to Couch Rotation in Stereotactic Radiation Surgery of Metastatic Brain Cancer
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Na Gwui-Geum
Park Byoung-Suk
Cha Woo-Jung
Park Yong-Chul
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Abstract
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Purpose: To purpose of this study is to find the correlation of the Set-up error according to the couch rotation and suggest additional margin setting for the GTV.
Target and Method: Each scenario treatment plan was created by making the frequency of non-coplanar beams different among all beams. The set-up error value was measured by using the Exact System and the dose accuracy was evaluated by creating a re-treatment plan.
Results: When the couch was rotated by 30°, 45°, 60°, and 90°, the mean of the X-axis values was measured to be 0.29 mm, 0.26 mm, 0.51 mm, and 0.08 mm, respectively. The mean of the Y-axis values was measured to be 0.75 mm, 0.5mm, 0.35 mm, and 0.29 mm, respectively. The mean of the Z-axis values was measured to be 0.5 mm, 0.28 mm, 0.22 mm, and 0.1 mm, respectively. There were dose reductions of 0.1%, 3.1%, 1.9% in D99 for 1-NC VMAT, 2-NC VMAT, and 3-NC VMAT, respectively.
Conclusion: When treating with 50% or more of non-coplanar beams among total beams, image verification is required. And it is considered to make the treatment plan by adding a 1.5 mm margin to the GTV.
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KEYWORD
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NC-VMAT, SRS, Couch rotation
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