Original MR-guided beam gating: Residual motion, gating efficiency and dose reconstruction for stereotactic treatments of the liver and lung

Purpose: This study aims to investigate the efficiency and the geometric as well as the dosimetric benefit of magnetic-resonance guided beam gating for stereotactic treatments in moving organs. Method: Patients treated with MR-guided (MRIdian system) SBRT for lung (n = 10) and liver (n = 10) tar-gets were analyzed. Breath-hold gating was performed based on lesion tracking in sagittal cine MRI images. The target offset from the geometric center of the gating window with and without gating was evaluated. A dose reconstruction workflow based on convolution of these 2D position-probability maps and the daily 3D dose distribution was used to estimate the daily delivered dose including motion. The dose to the clinical target volume (CTV) and to a 2-cm ring structure around the planning target vol-ume were evaluated.Results: The applied gating protocol resulted in a mean (+/- standard deviation) gating efficiency of 55%+/- 16%. Over all patients, the mean target offset (2D-root-mean-square error) was 8.3 +/- 4.3 mm, which reduced to 2.4 +/- 0.6 mm during gating. The dose reconstruction showed a mean deviation in CTV cover-age (D95) from the static plans of-1.7%+/- 1.8% with gating and-12.0%+/- 8.4% if no gating would have been used. The mean dose (Dmean) in the ring structure, with respect to the static plans, showed mean devi-ations of-0.1%+/- 0.3% with gating and-1.6%+/- 1.8% without gating. Conclusion: The MRIdian system enables gating based on the inner anatomy and the implemented dose reconstruction workflow demonstrated geometric robust delivery of the planned radiation doses.(c) 2022 The Author(s). Published by Elsevier B.V. Radiotherapy and Oncology 174 (2022) 101-108 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).