HighlightsDiscussion of DW imaging protocols and imaging setup.Discussion of mono- and bi-exponential models for quantitative parameter extraction.Review of recent publications investigating potential benefits of using DWI in RT, including detailed synoptic table.Detailed discussion of geometric and quantitative accuracy of DW imaging and DW-derived parameters.

Background and purposeFunctional PET/MRI has great potential to improve radiotherapy planning (RTP). However, data integration requires imaging with radiotherapy-specific patient positioning. Here, we investigated the feasibility and image quality of radiotherapy-customized PET/MRI in head-and-neck cancer (HNC) patients using a dedicated hardware setup.Material and methodsTen HNC patients were examined with simultaneous PET/MRI before treatment, with radiotherapy and diagnostic scan setup, respectively. We tested feasibility of radiotherapy-specific patient positioning and compared the image quality between both setups by pairwise image analysis of 18F-FDG-PET, T1/T2-weighted and diffusion-weighted MRI. For image quality assessment, similarity measures including average symmetric surface distance (ASSD) of PET and MR-based tumor contours, MR signal-to-noise ratio (SNR) and mean apparent diffusion coefficient (ADC) value were used.ResultsPET/MRI in radiotherapy position was feasible – all patients were successfully examined. ASSD (median/range) of PET and MR contours was 0.6 (0.4–1.2) and 0.9 (0.5–1.3) mm, respectively. For T2-weighted MRI, a reduced SNR of −26.2% (−39.0–−11.7) was observed with radiotherapy setup. No significant difference in mean ADC was found.ConclusionsSimultaneous PET/MRI in HNC patients using radiotherapy positioning aids is clinically feasible. Though SNR was reduced, the image quality obtained with a radiotherapy setup meets RTP requirements and the data can thus be used for personalized RTP.

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Multiparametric voxel-wise characterization of HNSCC is feasible using combined PET/MRI in a radiation planning setup. This technique may provide novel insights into tumour biology with regard to radiation therapy in the future.