Time trends in the maximal uptake of FDG on PET scan during thoracic radiotherapy. A prospective study in locally advanced non-small cell lung cancer (NSCLC) patients

Background and purpose18F-fluoro-2-deoxy-glucose (FDG) uptake on PET scan is a prognostic factor for outcome in NSCLC. We investigated changes in FDG uptake during fractionated radiotherapy in relation to metabolic response with the ultimate aim to adapt treatment according to early response.Methods and materialsTwenty-three patients, medically inoperable or with advanced NSCLC, underwent four repeated PET-CT scans before, during and after radiotherapy. Changes in maximal standardized uptake value (SUVmax) were described. Patients were treated with accelerated radiotherapy with a total tumour-dose depending on normal tissue dose constraints.ResultsThe most striking result was the large intra-individual heterogeneity in the evolution of SUVmax. For the total group a non-significant increase in the first week (p = 0.05), and a decrease in the second week (p = 0.02) and after radiotherapy (p < 0.01) was observed. Different time trends were shown for responders (no change during radiotherapy) and non-responders (48% increase during first week, p = 0.02 and 15% decrease in the second week, p = 0.04). Non-responders had a higher SUVmax on all time points investigated.ConclusionsTime trends in SUVmax showed a large intra-individual heterogeneity and different patterns for metabolic responders and non-responders. These new findings may reflect intrinsic tumour characteristics and might finally be useful to adapt treatment.