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 (rho). Dose painting plans were optimized based on the 50% isocontour of the maximum SUV (SUV50%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) mm(2)/s. The average rho between SUV and ADC was -0.2 (range: -0.6 to 0.4). The ADC-targets were only partly overlapping the SUV50%max-target and the dose parameters were significantly smaller in the ADC-targets compared to the SUV50%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. (C) 2013 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 106 (2013) 250-254