Early FDG-PET imaging after radical radiotherapy for non-small-cell lung cancer: inflammatory changes in normal tissues correlate with tumor response and do not confound therapeutic response evaluation.

PURPOSE To investigate the relationship between positron emission tomography (PET) detected inflammatory changes in irradiated normal tissues and metabolic response at tumor sites in patients receiving radical radiotherapy for non-small-cell lung cancer. The prognostic significance of these changes was also studied. METHODS In 73 consecutive patients, (18)F-fluorodeoxyglucose (FDG) PET was performed at a median of 70 days after completion of radical radiotherapy. Radiation-induced inflammatory change was scored for normal tissues within the radiation treatment volume using a 0-3 grading scale. Metabolic tumor response was assessed using a pattern-recognition algorithm comparing pre- and posttreatment scans. Prognostic significance of inflammatory changes was tested using the Cox proportional hazards regression model. RESULTS Increased FDG uptake in normal tissues (radiotoxicity) was associated with a greater likelihood of complete or partial tumor response on both PET (p = 0.0044) and computed tomography (p = 0.029). Prognostic stratification provided by PET response was both significant and of a similar magnitude in patients with low- and high-grade radiotoxicity. CONCLUSION Postradiotherapy inflammatory changes detected by FDG-PET are positively correlated with tumor response, suggesting that tumor radioresponsiveness and normal tissue radiosensitivity may be linked. Prognostic stratification provided by PET is not compromised by inflammatory changes if a meticulous visual response assessment technique is used.