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Daily IGRT QA Phantom for MR-Guided Linacs

D Moseley

D Moseley1,2*, T Stanescu1,2, (1) Princess Margaret Hospital, Toronto, ON, (2) University of Toronto, Toronto, ON

TH-A-BRA-3 Thursday 8:00:00 AM - 9:55:00 AM Room: Ballroom A

Purpose: To design a novel phantom compatible with multiple imaging modalities (kV, MV and MRI) for the daily quality assurance (QA) of an MR-guided linac.

Methods: At our institution, we are in the process of installing a decoupled MR-linac system, consisting of a 1.5T Siemens Espree MR scanner on rails that can be moved and image in the immediate proximity of a Varian TrueBeam linac. The two components are connected via a robotic patient couch. For this configuration, both MR and x-ray based (kV, MV) imaging modalities will be available and will have to be mutually correlated to confirm the robustness of the RT ensemble. The authors modified the design of on an existing daily QA phantom that is compatible with kV radiographs, MV EPIDs and kV CBCT. New features were added to make the phantom also visible on MRI. The overall design was optimized by means of numerical simulations to remove any significant MR image-related artifacts due to magnetic susceptibility-induced effects. An image software analysis tool was also developed to process the data and capture all kV/MV/MRI unique characteristics. In addition, the software provides the capability of record and track over time the performance of the tests via control charts.

Results: The phantom was developed to test kV/MV/MR system coincidence, 3D CBCT and 3D MR independent and cross-modality mutual registration, kV/MV and MR projection images, kV/MV coincidence, MR/linac laser and light field coincidence, remote table adjustments.

Conclusions: A novel phantom along with an image processing software package was developed for the routine daily QA of a linac-MR on rails radiotherapy system.

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