Work

Comprehensive motion management for liver SBRT on a 1.5 T MR-Linac: Initial clinical experience and dosimetric comparison with an ITV-based workflow

Year: 2026

Type: article

Abstract: Background and purpose Respiratory-gated MR-guided workflows enable expiration-gated liver stereotactic body radiotherapy (SBRT) based on real-time intrafraction target monitoring. We evaluated the dosimetric impact and early clinical feasibility of this approach by comparing clinically delivered expiration-gated plans with retrospectively generated non-gated ITV-based plans. Methods The first 20 consecutive patients treated with online adaptive MR-guided SBRT for primary or secondary liver malignancies on a 1.5 T MR-Linac between October 2024 and April 2025 were included. Five patients had two lesions, treated with separate plans in two patients, resulting in 22 matched plan pairs. For each clinically delivered gated plan, a retrospective ITV-based plan with identical prescription dose was generated. Paired differences were tested with the Wilcoxon signed-rank test, and p -values were adjusted for multiple testing using the Benjamini–Hochberg procedure. The dose–volume analysis was considered exploratory. Results Median planning target volume was lower with the gated workflow than with ITV-based planning (28.0 vs. 41.9 cc). Organ-at-risk constraint violations were fewer with the gated workflow (10 vs. 19), with 11 violations resolved and 2 newly occurring. PTV D98% did not differ significantly ( p = 0.41), although one gated and four ITV-based plans showed PTV D98% < 95%. Uninvolved liver dose was significantly lower with the gated workflow (median Dmean difference 0.97 Gy and 0.93 Gy for three- and five-fraction plans; adjusted p ≤ 0.037). Among 93 evaluable fractions, the mean plan-level median active delivery time was 7.6 min for three-fraction and 6.7 min for five-fraction treatments. Conclusion Expiration-gated MR-guided liver SBRT reduced target volumes and improved normal tissue sparing without compromising target coverage or routine clinical feasibility.

Source: Clinical and Translational Radiation Oncology

DOI: 10.1016/j.ctro.2026.101335