First-in-human technique translation of oxygen-enhanced MRI to an MR Linac system in patients with head and neck cancer

Background and purpose: Tumour hypoxia is prognostic in head and neck cancer (HNC), associated with poor loco-regional control, poor survival and treatment resistance. The advent of hybrid MRI - radiother-apy linear accelerator or 'MR Linac' systems - could permit imaging for treatment adaptation based on hypoxic status. We sought to develop oxygen-enhanced MRI (OE-MRI) in HNC and translate the tech-nique onto an MR Linac system.Materials and methods: MRI sequences were developed in phantoms and 15 healthy participants. Next, 14 HNC patients (with 21 primary or local nodal tumours) were evaluated. Baseline tissue longitudinal relaxation time (T1) was measured alongside the change in 1/T1 (termed AR1) between air and oxygen gas breathing phases. We compared results from 1.5 T diagnostic MR and MR Linac systems.Results: Baseline T1 had excellent repeatability in phantoms, healthy participants and patients on both systems. Cohort nasal concha oxygen-induced AR1 significantly increased (p < 0.0001) in healthy partic-ipants demonstrating OE-MRI feasibility. AR1 repeatability coefficients (RC) were 0.023-0.040 s-1 across both MR systems. The tumour AR1 RC was 0.013 s-1and the within-subject coefficient of variation (wCV) was 25% on the diagnostic MR. Tumour AR1 RC was 0.020 s-1and wCV was 33% on the MR Linac. AR1 magnitude and time-course trends were similar on both systems.Conclusion: We demonstrate first-in-human translation of volumetric, dynamic OE-MRI onto an MR Linac system, yielding repeatable hypoxia biomarkers. Data were equivalent on the diagnostic MR and MR Linac systems. OE-MRI has potential to guide future clinical trials of biology guided adaptive radiotherapy.(c) 2023 The Authors. Published by Elsevier B.V. Radiotherapy and Oncology xxx (2023) xxx-xxx This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).