An alternative parameter for early forecasting clinical response in NSCLC patients during radiotherapy: proof of concept study

Objective: Positron emission tomography with F-18 fludeoxyglucose integrated with CT (F-18-FDG PET/CT) is a recommended imaging procedure in the evaluation of non-small-cell lung cancers (NSCLCs). Radiochemotherapy (RCT) is a mainstay for treatment of locally advanced NSCLC, for which overall survival still remains poor. Early evaluation of treatment response may help in decision-making to complete radiotherapy (RT) or to switch to other treatment modalities. The present study aimed to evaluate the performance of new metabolic parameters based on a simplified kinetic analysis on a single time point (SKA-S)-derived mathematical method, as compared with standardized uptake value (SUV) measurement during RT. Methods: Four patients treated with RT or RCT for NSCLC were evaluated using F-18-FDG PET/CT during RT and after treatment completion. Whole-body F-18-FDG PET/CT was performed followed by four additional list-mode acquisitions centered over the target lesion. Response was evaluated at four times (i.e. PET1-PET4) by calculating standard SUV values and T80%, the time taken to reach 80% of F-18-FDG metabolized fraction using a SKA-S-derived mathematical method. Results: Data from SUV and T80% calculations were found to be controversial. T80% was found to be more predictive of clinical outcome. Conclusion: Although results from this pilot study should be further confirmed in a large prospective study, the data suggest that T80% is a promising metabolic biomarker for assessing early response to RT. Advances in knowledge: In this proof of concept study, we show that T80% defined from a mathematic model taking into account the net influx rate constant and vascular volume could be consider as a promising biomarker as compared with the maximum SUV.