This is a retrospective study encompassing all \[18F\]FET PET scans performed at our centre. By analysing both static and dynamic scans, conducting in-depth kinetic modelling, and comparing quantitative parameters across different tumour types and clinical contexts, the study aims to determine the true diagnostic value of \[18F\]FET PET in everyday clinical practice. The ultimate goal is to identify imaging biomarkers useful for improving tumour characterisation and distinguishing recurrence from post-treatment changes, thereby strengthening the role of \[18F\]FET PET in modern neuro-oncology.