ESTRO 2024 - Abstract Book

S3923

Physics - Image acquisition and processing

ESTRO 2024

Hence, relying exclusively on the rationale of mitigating MR-CT image registration uncertainties, the adoption of an MRI-only approach may not be an argument for intracranial tumours in general. It is important, however, to acknowledge that there are other advantages associated with MRI-only RT, which may confer supplementary benefits to all patients.

Keywords: Registration uncertainty, MRI-only, Brain tumours

2478

Mini-Oral

Developing geometrically robust diffusion-weighted MRI for head and neck imaging on an MR-Linac

Damien J. McHugh 1,2 , Alice Greenwood-Wilson 3 , Lisa McDaid 3 , Cynthia Eccles 3 , David Thomson 4 , David L. Buckley 1,5 , Ananya Choudhury 2,4 , Marcel van Herk 2 , Michael J. Dubec 1,2 1 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom. 2 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom. 3 The Christie NHS Foundation Trust, Radiotherapy Services, Manchester, United Kingdom. 4 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom. 5 University of Leeds, Biomedical Imaging, Leeds, United Kingdom

Purpose/Objective:

For functional information from diffusion-weighted (DW)-MRI to be used in adaptive radiotherapy for head and neck (H&N) cancer, DW images must have sufficient geometric accuracy. Typically used echo-planar imaging (EPI) readouts suffer from distortion [1], which motivates the use of alternative methods. This work compares two approaches to obtaining geometrically robust DW-MRI H&N acquisitions on an MR-Linac: distortion-corrected EPI [2,3] and split acquisition of fast spin-echo signals (SPLICE) [4].

Material/Methods:

All scans were performed on a 1.5 T MR-Linac (Elekta Unity). Phantom imaging was performed using the CaliberMRI NIST/QIBA Diffusion Phantom to compare apparent diffusion coefficient (ADC) values for EPI and SPLICE acquisitions against the ground truth. Patient volunteer imaging was performed to evaluate the effectiveness of the EPI distortion correction for H&N tumours, and compare this with SPLICE. Patients provided informed consent, and were recruited to the PRIMER study (IRAS ID: 208449). For all scans, the imaging protocol included a T2-weighted anatomical scan, the MRL Consortium Consensus H&N DW-MRI EPI sequence (voxel size = 3.5 x 3.5 x 4.0 mm 3 , 30 slices, b -values (averages) = 0 (2), 150 (4), 500 (12) s/mm 2 , TR = 4308 ms, TE = 75 ms, scan time = 3:40), and a SPLICE sequence (voxel size = 3.5 x 3.5 x 4.0 mm 3 , 18 slices, b values (averages) = 0 (4), 150 (6), 500 (12) s/mm 2 [1], TR = 3516 ms, TE = 83 ms, scan time = 6:48). The EPI sequence was run twice with opposing phase-encoding (PE) directions to enable distortion correction [2], as implemented in the topup tool in the Functional MRI of the Brain Software Library (FSL) [5,6]. Two methods of applying topup using