Implementation of FDG-PET/CT imaging methodology for quantification of inflammatory response in patients with locally advanced non-small cell lung cancer: results from the ACRIN 6668/RTOG 0235 trial.

We measured changes in 18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) images in the lung parenchyma to quantify the degree of lung inflammation in patients with locally advanced non-small cell lung cancer (NSCLC) who received radiotherapy (RT). The goal of this study was to demonstrate successful implementation of this imaging methodology on NSCLC patients and to report quantitative statistics between pre-RT and post-RT. Seventy-one patients with NSCLC underwent FDG-PET/CT imaging before and after RT in a prospective study (ACRIN 6668/RTOG 0235). Comparisons between pre-RT and post-RT PET/CT were conducted for partial volume corrected (PVC)-mean standardized uptake value (SUVmean), PVC-global lung parenchymal glycolysis (GLPG), and lung volume for both ipsilateral and contralateral lungs using the nonparametric Wilcoxon signed-rank test. Regression modeling was conducted to associate clinical characteristics with post-RT PET/CT parameters. There was a significant increase in average SUVmean and GLPG of the ipsilateral lung (relative change 40% and 20%) between pre-RT and post-RT PET/CT scans (P<0.0001 and P=0.004). Absolute increases in PVC-SUVmean and PVC-GLPG were more pronounced (ΔPVC-SUVmean 0.32 versus ΔSUVmean 0.28; ΔPVC-GLPG 463.34 cc versus ΔGLPG 352.90 cc) and highly significant (P<0.0001). In contrast, the contralateral lung demonstrated no significant difference between pre-RT to post-RT in either GLPG (P=0.12) or SUVmean (P=0.18). The only clinical feature significantly associated with post-RT PET/CT parameters was clinical staging. Our study demonstrated inflammatory response in the ipsilateral lung of NSCLC patients treated with photon RT, suggesting that PET/CT parameters may serve as biomarkers for radiation pneumonitis (RP).