Purpose: FDG PET is frequently used for radiotherapy (RT) planning to determine the tumour extent. Similarly, FMISO is used to assess the hypoxic sub-volume. The relationship between the volumes determined on the basis of FDG and FMISO was investigated. Additionally, the quantitative correlation of the tracers on a voxel basis was studied.
Methods: Twelve head-and-neck cancer (HNC) patients underwent FDG and FMISO PET examinations prior to RT treatment. The tumour volumes assessed by the two tracers and also the voxel-based joint uptake values were investigated. The characteristic shapes and patterns of the determined scatter plots were analyzed. A number of different variables such as the maximum uptake values of FDG and FMISO, the FDG and FMISO positive volumes, the slope m of the regression line and the scatter width sigma of the scatter plots were tested for their ability to stratify the patient group with respect to treatment outcome.
Results: A diversity of characteristic FDG-FMISO distributions was observed in the patient group. However, no general correlation of enhanced glucose metabolism and FMISO uptake was observed. The maximum uptake of FMISO (p=0.045) showed borderline significance for stratifying the patient group. FDG positive tumour volume, hypoxic fraction, maximum FDG uptake and m were not significant. Sigma turned out to be the most significant variable (p=0.008) to predict treatment success probabilities.
Conclusion: FMISO and FDG PET data provide independent information about the examined tumour. A quantification of the correlated tracer uptake seems to be meaningful.