Keywords: Simulation/Validation, Diffusion/other diffusion imaging techniques, MR-linac, image-guided radiation therapy, repeatability
Motivation: In order to use DWI on MR-linacs to adapt head and neck cancer radiotherapy treatment plans based on response, the variability in ADC must be characterized.
Goal(s): To quantify the repeatability of ADC on a 1.5T MR-linac in a large cohort (37 head and neck cancer patients).
Approach: Patients were imaged with echo planar imaging-DWI twice before the start of radiotherapy. Mean ADC values of primary tumors and lymph nodes were compared across time points using repeatability metrics.
Results: Repeatability coefficients were 53.0%/35.5% for tumors/nodes, indicating that this DWI sequence is insufficient for detecting clinically significant ADC changes and must be further optimized.
Impact: Our DWI test-retest results demonstrate that the current widely implemented EPI-DWI sequence for head and neck cancers on 1.5T MR-linacs has substantial ADC variability across time points and needs to be further refined.
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