Pathological complete response and tumor regression to less than 10% vital tumor cells after induction chemoradiotherapy have been shown to be prognostically important in non-small cell lung cancer (NSCLC). Predictive imaging biomarkers could help treatment decision-making. The purpose of this study was to assess whether postinduction changes in tumor FDG uptake could predict pathological response and to evaluate the correlation between residual vital tumor cells and post-induction FDG uptake.

METHODS: NSCLC patients with sulcus superior tumor (SST), planned for trimodality therapy, routinely undergo FDG PET/CT scans before and after induction chemoradiotherapy in our institute. Metabolic end-points based on standardized uptake values (SUV) were calculated, including SUVmax (maximum SUV), SUVTTL (tumor-to-liver ratio), SUVpeak (SUV within 1 cc sphere with highest activity), and SUVPTL (peak-to-liver ratio). Pathology specimens were assessed for residual vital tumor cell percentages and scored as no (grade 3), <10% (grade 2b) and >10% vital tumor cells (grade 2a/1).

RESULTS: 19 and 23 patients were evaluated for (1) metabolic change and (2) postinduction PET-pathology correlation, respectively. Changes in all parameters were predictive for grade 2b/3 response. ΔSUVTTL and ΔSUVPTL were also predictive for grade 3 response. Remaining vital tumor cells correlated with post-induction SUVpeak (R=0.55; P=0.007) and postinduction SUVPTL (R=0.59; P=0.004). Postinduction SUVPTL could predict both grades 3 and 2b/3 response.

CONCLUSION: In NSCLC patients treated with chemoradiotherapy, changes in SUVmax, SUVTTL, SUVpeak, and SUVPTL were predictive for pathological response (grade 2b/3 and for SUVTTL and SUVPTL grade 3 as well). Postinduction SUVPTL correlated with residual tumor cells.