The Beneficial Value of PET/CT in the Follow-up of Stage III Non-small Cell Lung Cancer Patients

Stage III non-small cell lung cancer (NSCLC) patients are at high risk of developing recurrences (50-78%) during follow-up. With more effective treatments available for patients with oligometastatic disease, early detection of tumor recurrence can prolong survival and health-related quality of life and thereby lower the disease burden. With the use of 18F FDG PET/CT during follow-up, recurrences may be detected earlier at an oligometastatic state when curative-intent treatment is still possible. Primary objective: \- The primary objective of this study is to compare the 3-year overall survival of stage III NSCLC patients during follow-up surveillance with 18F FDG PET/CT versus follow-up with conventional CT surveillance. The secondary objectives of this study are: * To compare the 2-year overall survival of stage III NSCLC patients during follow-up surveillance with 18F FDG PET/CT versus follow-up with conventional CT-based surveillance (interim analysis); * To compare the number of detected (symptomatic and asymptomatic) recurrences of stage III NSCLC patients during follow-up surveillance with 18F FDG PET/CT versus follow-up with conventional CT-based surveillance; * To compare the event-free survival of stage III NSCLC patients during follow-up surveillance with 18F FDG PET/CT versus follow-up with conventional CT-based surveillance; * To determine the cost-effectiveness of 18F FDG PET/CT versus conventional CT-based surveillance during follow-up of stage III NSCLC patients; * To compare the effect of 18F FDG PET/CT versus conventional CT-based surveillance on health-related quality of life during follow-up of stage III NSCLC patients; * To assess the beneficial value of ctDNA in the detection of recurrences during follow-up in stage III NSCLC patients; * To identify patients' experiences with the additional 18F FDG PET/CT scans in the follow-up of stage III NSCLC patients. * To assess differences in type of treatment following recurrence during follow-up in stage III NSCLC patients. Primary analyses will be performed on an intention-to-treat basis as well as per protocol. Kaplan-Meier curves with stratified log-rank 2-sided tests will be used to compare the survival between groups. In case of empty strata, strata will be collapsed. The clinical relevance of the difference will be primarily expressed in terms of 3-year survival of the intervention versus the control group.