When is it Best to Repeat a 2-Fluoro-2-Deoxy-d-Glucose Positron Emission Tomography/Computed Tomography Scan on Patients with Non-Small Cell Lung Cancer Who Have Received Neoadjuvant Chemoradiotherapy?

Background The ideal time to repeat a 2-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET)/computed tomography (CT) scan to accurately restage a patient after neoadjuvant chemoradiotherapy for non-small cell lung cancer (NSCLC) is unknown. Methods This retrospective cohort study used a prospective database of patients who underwent neoadjuvant chemoradiotherapy, an initial and repeat FDG-PET/CT scan, and pathologic staging. The accuracy of the clinical stage suggested by repeat FDG-PET/CT was compared with the actual pathologic stage. Receiver operating characteristic (ROC) curves were used to determine when it was most accurate to repeat the FDG-PET/CT after the completion of the last dose of chest radiation. Results The study comprised 109 patients, 93 of whom patients received 60 Gy (or higher) of radiotherapy. The median time to restaging was 24 days (range, 2 to 88 days). ROC analysis showed the optimal time to restage patients was 26 days for overall staging (area under the curve [AUC], 0.88) and 29 days for N2 restaging (AUC, 0.82). The accuracy for overall stage was 3 (38%) of 8 for patients for less than 10 days, 28 (72%) of 39 for patients between 11 and 20 days, 42 (88%) of 49 between 21 and 30 days, and 8 (62%) of 13 for 31 days or more. The accuracy for these time intervals for the restaging of the N2 lymph node was 50% (1/2) 40% (2/5), 88% (7/8), and 100% (3/3), respectively. Conclusions The optimal time to perform a repeat FDG-PET/CT scan after the completion of neoadjuvant chemotherapy and high-dose radiotherapy to maximize its accuracy for restaging patients with NSCLC is about 1 month after the last dose of radiation.