FDG-PET and diffusion-weighted MRI in head-and-neck cancer patients: Implications for dose painting

Purpose: The purpose of this study was to investigate if FDG-PET and DWI identify the same or different targets for dose escalation in the GTV of HN cancer patients. Additionally, the dose coverage of DWI-targets in an FDG-PET-based dose painting plan was analyzed. Materials and methods: Eighteen HN cancer patients underwent FDG-PET and DWI exams, which were converted to standardized uptake value (SUV)- and apparent diffusion coefficient (ADC)-maps. The correspondence between the two imaging modalities was determined on a voxel-level using Spearman's correlation coefficient (ρ). Dose painting plans were optimized based on the 50% isocontour of the maximum SUV (SUV _50%max). Dose coverage was analyzed in three different SUV- and three different ADC-targets using the mean dose and the near-minimum and near-maximum doses. Results: The average maximum SUV was 13.9 and the mean ADC was 1.17 · 10^-3 mm²/s. The average ρ between SUV and ADC was -0.2 (range: -0.6 to 0.4). The ADC-targets were only partly overlapping the SUV_50%max-target and the dose parameters were significantly smaller in the ADC-targets compared to the SUV_50%max-target. Conclusions: FDG-PET and DWI contain different information, resulting in different targets. Further information about failure patterns and dose relations can be obtained by adding DWI to currently ongoing dose painting trials.