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Commissioning of the Elekta VersaHD Linear Accelerator

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Y Zhang

Y Zhang1*, K Ding1 , R Hobbs1 , X Liang2 , T Zhu2 , T McNutt1 , K Wang1 , (1) Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, School of Medicine, Baltimore, MD (2) Department of Radiation Oncology, University of Pennsylvania, School of Medicine, Philadelphia, PA


SU-E-T-74 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To present the commissioning process of recently-released Elekta VersaHD linear accelerator, equipped with Agility 160-leaf multileaf collimator and flattening-filter free (FFF) photon modes.

Methods: In addition to routine QA procedures, we adopted an EPID-based method to perform the table rotation and Winston-Lutz tests, and a novel multi-radiation isocenter alignment check. The beam data acquired include photon percent-depth dose (PDD) of 6X, 6XFFF, 10X, 10XFFF, and 15X in the field size from 2x2 to 40x40cm², profiles, collimator and phantom scatter factors (Sc and Sp), wedge factor, electron (6, 9, 12, and 15MeV) PDD and profiles, cone and cutout factors, and virtual SSD. Validation measurements were carried out in water tank to evaluate the accuracy of beam modeling by the Pinnacle planning system. End-to-End test and IMRT QA were performed to validate the overall delivery accuracy. A theoretical model has also been used to extract the primary dose ratio and off-axis beam softening effects by fitting photon beam profile measurements.

Results: The PDDs of FFF beams with field size 10x10cm² at 10cm depth, 100cm SSD were intentionally adjusted within 1% of the non-FFF beams. The photon profiles of 30x30cm² at 10cm depth between non-FFF and FFF beams are very different, OAR(10)=0.74 and 0.63, respectively, for 6XFFF and 10XFFF. The collimator and phantom scatter factors of FFF beam demonstrated smaller variation with field sizes. The EPID-based method demonstrated the maximum deviation between the table rotation axis and radiation isocenter is within 1mm, and the radiation isocenters are within 0.4mm relative to that of 6X. The validation measurement shows less than 2% deviation between the measurement and Pinnacle modeling for most of the test conditions.

Conclusion: To the best of our knowledge, this is the first study reporting the Elekta VersaHD commissioning experience, which can be a valuable reference for the radiotherapy community.

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