ESTRO 2025 - Abstract Book

S4374

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

3369

Proffered Paper Towards clinical introduction of T2-TSE-cine images for an intrafraction drift correction workflow for pelvis treatments on the Unity MR-Linac Lieke T.C. Meijers 1 , Johannes C.J. de Boer 1 , Jochem R.M. van de Voort van Zyp 1 , Nicole G.P.M. Vissers 1 , Reijer H.A. Rutgers 1 , Eveline Alberts 2 , Alice M. Couwenberg 3 , Martijn P.W. Intven 1 , Bas W. Raaymakers 1 , Astrid L.H.M.W. van Lier 1 1 Radiotherapy, UMC Utrecht, Utrecht, Netherlands. 2 Healthcare, Philips, Eindhoven, Netherlands. 3 Radiotherapy, NKI-AVL, Amsterdam, Netherlands Purpose/Objective: Comprehensive Motion Management (CMM) gives the possibility to correct for intrafraction motion during treatment on the Unity MR-Linac (Elekta AB, Stockholm, Sweden). CMM provides interleaved coronal and sagittal balanced Turbo Field Echo (bTFE) 2D-images of 5 Hz, characterized by high SNR, but limited by image contrast in the pelvis and contains sequence specific image artifacts especially due to air pockets in the rectum. This abstract reports about evaluation of a new MRI sequence with T2-weighted contrast and without image artifacts which can be used in CMM to capture and correct for intrafraction motion of pelvic targets in terms of gating accuracy, visual grading scores and acoustic noise levels. Material/Methods: Cine imaging was acquired within 86 fractions of 52 patients with tumors in the prostate, rectum and pelvic oligolymphnode metastases (LNM). The standard bTFE-cine (TR:3.4, TE:1.7, resolution 3.0x3.0x5.0mm, imaging frequency 5Hz) and the new T2-TSE-cine (TR:2000, TE:150, 2.0x2.0x5.0mm, 0.5Hz) images were acquired during approximately 12.3 minutes per session on the MR-Linac. Before and after cine acquisition, T2-weighted 3D images were acquired and manually rigidly registered on the target (3D-3D registration). Registration was automatically performed between the 3D pre-scan and the last 10 seconds of the 2D-cine acquisition in CMM (3D-2D registration). The deviations between the 3D-3D and 3D-2D registration were measured in LR, AP and SI-direction and compared for the bTFE- and T2-TSE-cine. Furthermore a Visual Grading Assessment (VGA) was performed for both acquisitions within 16 prostate-, rectum- or LNM- cancer patients, where image quality was scored by 5 experts. In addition acoustic noise measurements were performed in the center of the bore.

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