ESTRO 2025 - Abstract Book

S3291

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

ESTRO 2025

Conclusion: We successfully performed the world’s first online, real-time dose reconstruction for prostate and bladder, incorporating motion during prostate SBRT. MV-kV guidance effectively mitigated severe motion-induced dose distortions.

Keywords: Motion-including dose, prostate SBRT

References: [1] Hunt MA, Sonnick M Fau - Pham H, Pham H Fau - Regmi R, Regmi R Fau - Xiong J-p, Xiong Jp Fau - Morf D, Morf D Fau - Mageras GS, et al. Simultaneous MV-kV imaging for intrafractional motion management during volumetric modulated arc therapy delivery. J Appl Clin Med Phys. 2016. [2] Ravkilde T, Skouboe S, Hansen R, Worm E, Poulsen PR. First online real ‐ time evaluation of motion ‐ induced 4D dose errors during radiotherapy delivery. Medical Physics. 2018;45:3893-903 [3] Poulsen PR, Cho B, Keall PJ. Real-time prostate trajectory estimation with a single imager in arc radiotherapy: a simulation study. Physics in Medicine and Biology. 2009;54:4019-35

3054

Digital Poster Dosimetric impact of delivering beams lateral first vs. clockwise order for prostate SABR with 1.5T MR-Linac Akos Gulyban 1 , Zelda Paquier 1 , Christelle Bouchart 2 , Madeline Michel 2 , Nicolas Jullian 2 , Sara Poeta 1 , Robbe Van den Begin 2 , Nick Reynaert 1 1 Medical Physics, Institute Jules Bordet, Brussels, Belgium. 2 Radiation Oncology, Institute Jules Bordet, Brussels, Belgium Purpose/Objective: During MR guided online adaptive prostate stereotactic ablative radiotherapy (SABR), the largest concern regarding intrafraction motion is the prostate movement, primarily in the antero-posterior direction due to increased bladder filling and/or rectal shape variation. Our aim was to evaluate the dosimetric impact of prioritizing delivery of beams with the most sensitivity to antero posterior movements (“lateral first”, LF), rather than using the classical clockwise (CW) beam sequencing during step and shoot IMRT.

Material/Methods: Twenty prostate patients treated with SABR with 36.25/40 Gy in 5 fractions for PTV/CTV using 1.5 T MR-Linac daily online adaptive workflow were included in this study. All cases were planned with the same template using 9 beams based on T2 2 min TSE MRI image sets. Clinical treatment delivery was executed by treating the lateral beams prior to the remaining angles, kept in a clockwise order (LF Gantry angle order: 100, 70, 290, 260, 210, 320, 0, 40, 150).