Rapid distortion correction enables accurate magnetic resonance imaging-guided real-time adaptive radiotherapy

Paul Z Y Liu; Shanshan Shan; David Waddington; Brendan Whelan; Bin Dong; Gary Liney; Paul Keall

doi:10.1016/j.phro.2023.100414

Rapid distortion correction enables accurate magnetic resonance imaging-guided real-time adaptive radiotherapy

Phys Imaging Radiat Oncol. 2023 Jan 21:25:100414. doi: 10.1016/j.phro.2023.100414. eCollection 2023 Jan.

Authors

Paul Z Y Liu^{1

2}, Shanshan Shan^{1

2}, David Waddington^{1

2}, Brendan Whelan^{1

2}, Bin Dong², Gary Liney^{2

3

4}, Paul Keall^{1

2}

Affiliations

¹ Image X Institute, University of Sydney Central Clinical School, Sydney, NSW, Australia.
² Department of Medical Physics, Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia.
³ School of Medicine, University of New South Wales, Sydney, NSW, Australia.
⁴ Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.

Abstract

Background and purpose: Magnetic resonance imaging (MRI)-Linac systems combine simultaneous MRI with radiation delivery, allowing treatments to be guided by anatomically detailed, real-time images. However, MRI can be degraded by geometric distortions that cause uncertainty between imaged and actual anatomy. In this work, we develop and integrate a real-time distortion correction method that enables accurate real-time adaptive radiotherapy.

Materials and methods: The method was based on the pre-treatment calculation of distortion and the rapid correction of intrafraction images. A motion phantom was set up in an MRI-Linac at isocentre (P₀ ), the edge (P ₁) and just outside (P ₂) the imaging volume. The target was irradiated and tracked during real-time adaptive radiotherapy with and without the distortion correction. The geometric tracking error and latency were derived from the measurements of the beam and target positions in the EPID images.

Results: Without distortion correction, the mean geometric tracking error was 1.3 mm at P ₁ and 3.1 mm at P ₂. When distortion correction was applied, the error was reduced to 1.0 mm at P ₁ and 1.1 mm at P ₂. The corrected error was similar to an error of 0.9 mm at P₀ where the target was unaffected by distortion indicating that this method has accurately accounted for distortion during tracking. The latency was 319 ± 12 ms without distortion correction and 335 ± 34 ms with distortion correction.

Conclusions: We have demonstrated a real-time distortion correction method that maintains accurate radiation delivery to the target, even at treatment locations with large distortion.

Keywords: DSV, diameter of spherical volume; EPID, electronic portal imaging device; GNL, gradient non-linearity; MLC tracking; MLC, multi-leaf collimator; MRI distortion; MRI, magnetic resonance imaging; MRI-Linac; RMSE, root-mean-square error; Real-time adaptive radiotherapy.