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Geometric and Dosimetric Accuracy for Non-Coplanar VMAT with Continuous Couch Rotation Using L-Shaped Treatment Machine

H Hirashima*, M Nakamura, Y Miyabe, N Mukumoto, T Mizowaki, Graduate School of Medicine, Kyoto University.


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 7

Purpose: Non-coplanar VMAT is efficient for sparing doses to organs-at-risk. Currently, non-coplanar VMAT with continuous couch rotation (CCR-VMAT) is deliverable via developer mode by using L-shaped linear accelerator, the most common type of radiation treatment machine. The purpose of this study was to assess geometric and dosimetric accuracy of CCR-VMAT.

Methods: CCR-VAMT plans for five prostate cancer patients were generated in commercially available TPS. Subsequently, dosimetric QA plans were imported in developer mode in XML file format, and QA was then performed. Following indices were analyzed to delivery accuracy of CCR-VMAT. First, geometric accuracy were evaluated by using logfile. Root mean square errors (RMSEs) between actual and planned values in logfile, which recorded mechanical information at 20 ms intervals, were calculated for gantry angle, couch angle, MLC position and MU, respectively. In addition, with respect to the steel ball center at each gantry and couch angle, the X- and Y-axis deviation from the MV beam center were calculated by using EPID images. Next, dosimetric QA was performed with 3D diode detector, and the passing rates for γ with criteria of 1%/1 mm, 2%/2 mm and 3%/3 mm were calculated.

Results: Seven continuous non-coplanar trajectories without collision were used. The median values of RMSEs for the gantry angle, couch angle, MLC position, and MU were 0.04° (range, 0.04°–0.05°), 0.07° (range, 0.03°–0.09°), 0.03 mm (range, 0.03–0.03 mm), and 0.01 MU (range, 0.01–0.01 MU), respectively. The deviation of the MV beam center from the steel ball center was less than 1.0 mm. The median passing rates for γ with criteria of 1%/1 mm, 2%/2 mm, and 3%/3 mm were 63.9% (range, 53.4%–68.0%), 91.2% (range, 87.7%–94.4%), and 98.2% (range, 95.7%–99.3%), respectively.

Conclusion: Performance of CCR-VMAT via developer mode was stable regardless of trajectories.

Funding Support, Disclosures, and Conflict of Interest: This research was supported in part by the Practical Research for Innovative Cancer Control (17ck0106151h0003), as part of the Japan Agency for Medical Research and Development, AMED.


Not Applicable / None Entered.


TH- External beam- photons: Development (new technology and techniques)

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