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Development of New MLC QA of Volumetric Modulated Arc Therapy Using a High Sampling Rate Log File

S Nishiyama*, M Seo , K Makabe , M Kuramochi , T Suzuki , H Tomita , Dept. of Radio Technology, Saiseikai Kawaguchi General Hospital, Kawaguchi, Saitama


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: We developed a new method to evaluate the MLC position errors in VMAT using a high sampling rate log file (HLF) output from Elekta's Synergy with Agility.

Methods: Systematic errors were calculated from the ratio between the travel areas of MLC A, B, and Gap from the HLF and the same areas of Dicom-RT plan using an in-house software. In the prostate VMAT plan, we added the known errors (Open: 0.1, 0.2, 0.5, 1.0 mm, Close: -0.1, -0.2, -0.5, -1.0 mm) to the moving MLC and evaluated the ability to detect errors through our new method. At the same time, a gamma pass ratio was obtained from Delta 4 device. The MLC errors obtained from our method were compared with the gamma pass ratio. In addition we evaluated 105 irradiations of 3 prostate VMAT plans.

Results: Correlation coefficients of errors detection of our method for all known MLC errors were all 0.99 in MLC A, B and Gap. When the known error was -1.0 mm, the maximum error of MLC A, B and Gap was -0.46mm, 0.48mm and 0.94 mm. The gamma pass ratio was less than 95% when the MLC error was 0.5mm, 1.0mm and -1.0 mm. In the prostate VMAT Plan, the mean errors of MLC A, B and Gap were -0.025mm, 0.033mm and 0.059mm.It was possible to detect MLC systematic errors using an HLF. We were able to confirm the detailed control of MLC and slight errors between the treatment planning system and linac using an HLF. The prostate VMAT plan was adequately irradiated with an accuracy of less than 0.1 mm.

Conclusion: We developed a new method to evaluate the MLC position errors from an HLF output from Synergy with Agility.


MLC, Quality Assurance, Intensity Modulation


TH- External beam- photons: Quality Assurance - IMRT

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