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KMID : 1164220170290020083
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Journal of Korean Society for Radiotherapeutic Technology
2017 Volume.29 No. 2 p.83 ~ p.91
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Comparative evaluation for leaf position accuracy according to gantry angle variation in MLC quality assurance using electronic portal imaging device(EPID) and GafChromic EBT3 film
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Yang Myung-Sic
Park Ju-Kyeong
Lee Seung-Hun
Lee Sun-Young
Kim Jung-Soo
Kwon Hyoung-Cheol
Kim Yang-Su
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Abstract
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Objectives: The purpose of this study was to evaluate the error of the leaf position accuracy of the MLC due to the gravity effect according to the gantry angle by using picket fence test using EPID and GafChromic EBT3 film. Materials and
Methods: A 5 cm solid phantom was placed on the table and the SAD was set to 100 cm. The EBT3 film was placed exactly over the solid phantom and covered a 1.5 cm solid phantom and the picket fence test was performed. The EPID was measured under the same conditions as the EBT3 film at SID 100 cm. The gantry angles were measured at 0 ? 0? , 90 ? 90? , 180 ? 180? and 270 ? 270? in order to evaluate the position of the MLC according to the gantry angle. For the geometric evaluation of the MLC, the leaf position accuracy of the MLC was analyzed using the analysis program.
Results: In case of EPID, when the gantry angle was changed to 0 ? 0? , 90 ? 90? , 180 ? 180? , 270 ? 270? , the difference of the position errors of the leaves was 0.18 mm, 0.31 mm, 0.20 mm, 0.26 mm on the average and the maximum values of the errors were respectively 0.44 mm, 0.54 mm, 0.34 mm, 0.44 mm. In case of EBT3 film, when the gantry angle was changed to 0 ? 0? , 90 ? 90? , 180 ? 180? , 270 ? 270? , the difference of the position errors of the leaves was 0.19 mm, 0.21 mm, 0.19 mm, 0.31 mm on the average and the maximum values of the errors were respectively 0.35 mm, 0.45 mm, 0.36 mm, 0.48 mm.
Conclusion: In this study, we analyzed the position error of the leaf of the MLC according to the gantry angle, and confirmed the position error of the leaf by gravity effect. As a result of comparing the leaf position accuracy using EPID and EBT3 film according to the variation of gantry angle, a larger error occurred in the error analysis method using EPID than that of EBT3 film. Therefore, in the case of IMRT based on MLC, as well as verification of accurate dosimetry should be conducted, it is considered that the quality control and verification for the precise operation of the MLC will be needed. and it is necessary to compare and verify the method of analysis.
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KEYWORD
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EPID , EBT3 film , MLC , Gantry angle , Gravity effect , Quality assurance
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