Prognostic Value of FDG PET Metabolic Parameters Before and After 42 Gy of Radiochemotherapy in Patients with Inoperable Stage III Nonsmall Cell Lung Cancer

The purpose of this study was to assess the prognostic value of ¹⁸F-FDG PET parameter variation between baseline and 42 Gy (PET2) of radiochemotherapy at 6 mo and 1 y of evaluation in patients with stage III inoperable nonsmall cell lung cancer based on RECIST 1.1. Methods: In total, 158 patients in a prospective multicenter phase II/III study were analyzed. Patients were randomized into 2 groups: an experimental arm (group A) and a standard arm (group B). Patients from group A with residual metabolism on PET2 (group A+) at 42 Gy received a radiation boost (74 Gy). Patients without residual uptake on ¹⁸F-FDG PET at 42 Gy (group A−) and patients in group B received a standard radiotherapy dose (66 Gy). We compared group A with group B. The ¹⁸F-FDG PET parameters SUV_max, SUV_mean, SUV_peak, peak SUV normalized on lean body mass, mean SUV normalized on lean body mass, total lesion glycolysis, total metabolic tumor volume (MTV) (tumor and nodes), and tumor MTV were measured. All patients were evaluated with RECIST 1.1 using CT at 6 mo and 1 y after radiochemotherapy. Progression-free survival and overall survival were evaluated. Results: Except for the radiotherapy dose (P < 0.001), patient demographic characteristics were similar between the 2 groups (A vs. B). All ¹⁸F-FDG PET uptake and volume parameter measurements were correlated. Therefore, only the change in SUV_max (ΔSUV_max) and total MTV were selected for the analysis. There was no significant difference in any variable between the 2 groups. In the multivariate analysis, ΔSUV_max appeared to be the most important prognostic factor for overall survival, and SUV_max of PET2 appeared to be the most important prognostic factor for progression-free survival. Conclusion:¹⁸F-FDG PET at 42 Gy can be used to identify good responders to radiochemotherapy in patients with inoperable stage III nonsmall cell lung cancer. The SUV_max of PET2 and ΔSUV_max are independent prognostic factors.