Rapid distortion correction enables accurate magnetic resonance imaging-guided real-time adaptive radiotherapy. (January 2023)

• Record Type: Journal Article
• Authors: Liu, Paul Z. Y; Shan, Shanshan; Waddington, David; Whelan, Brendan; Dong, Bin; Liney, Gary; Keall, Paul
• Is Part Of: Physics and imaging in radiation oncology. Volume 25(2023)
• Publication Date: 2023-01
• Subjects: MRI distortion -- MLC tracking -- MRI-Linac -- Real-time adaptive radiotherapy; DSV diameter of spherical volume -- EPID electronic portal imaging device -- GNL gradient non-linearity -- MLC multi-leaf collimator -- MRI magnetic resonance imaging -- RMSE root-mean-square error; Radiotherapy -- Periodicals; Radiation dosimetry -- Periodicals; Cancer -- Imaging -- Periodicals; Oncology -- Periodicals; 615.842
• DOI: 10.1016/j.phro.2023.100414
• Languages: English
• ISSNs: 2405-6316

Abstract

Highlights: Magnetic resonance imaging (MRI) can be affected by geometric distortions. Distortion degrades the accuracy of tracking tumor motion during radiotherapy. The correction of distortion can be rapidly applied during treatment. Tumor tracking using corrected images achieves the required geometric accuracy. 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.