Lung cancer is one of the most common forms of cancer, accounting for 13% of all diagnosed cancers (around 1.6 million new cases per year woldwide), and for 18% of all cancer-related deaths. Despite considerable improvements in the treatment options for advanced-stage and metastatic lung cancer, disease-specific survival remains poor. With the aim of improving patients outcome, the treatment paradigm of locally advanced lung cancer has shifted from solely radiotherapy towards combined and intensified treatment approaches. However, personalizing treatment to the individual patient remains difficult and requires monitoring of biological parameters responsible for treatment resistance to facilitate treatment selection, guidance, and adaption. Positron emission tomography (PET) is a well established molecular imaging platform that enables non-invasive quantification of many biological parameters that are relevant to both local and systemic therapy. In this thesis, the possibilities and methodological considerations of PET in combination with X-ray computed tomography (CT) imaging with the glucose analogue 18F-fluordeoxyglucose (FDG) in oncological management of patients with lung cancer were further explored.