ESTRO 2025 - Abstract Book

S3248

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

The 3D Vane XD SPAIR was identified as the MR protocol for superior visualization of the mesenteric mass. Relative to the dry-run’s tumor position, the daily tumor displacement ranged from 1.48 cm posterior to 3.83 cm anterior, 0.88 cm inferior to 3.26 cm superior, and 5.42 cm right to 12.42 cm left. The tumor shape was highly irregular and changed daily with a complexity of 1.8±0.2. Tumor volume increased from 16.7 cc (fraction 1) to 44.2 cc (fraction 6), followed by a downward trend. Fractions 10 and 11 images showed the tumor diminishing, so fraction 12 was canceled. ATS planning produced high-quality plans with a CI of 0.88±0.02 and the HI consistently at 1.07. D 0.1cc to the spinal canal, left and right kidney were 387±45, 369±107, and 349±161 cGy, respectively. Conclusion: Conventional radiotherapy with a static treatment plan cannot accurately cover a target with unpredictable and significant inter-fraction motion, unless extremely large margins are applied. In contrast, MR-Linac enabled real time tailored treatments with superior target coverage while minimizing dose to organs-at-risk. For the first time, we treated a mesenteric mass that moved by almost 20 cm laterally with significant shape and volume changes.

Keywords: MR-Linac, Mesenteric Mass