Tyrosine-kinase Inhibitors (TKI) resistance in gastrointestinal stromal tumours (GIST) is a common problem after prolonged treatment periods. The main objectives of this monocentric diagnostic Phase I/IIa study are safety and tolerability, pharmacokinetics and dosimetry of 68Ga-NeoBomb1 in GIST patients. The rationale behind this study is to improve diagnostic accuracy in GIST via positron-emission tomography/computer tomography (PET-CT) with a focus on TKI-resistant subtypes. Better detection, classification and definition of lesion extent are expected from the use of 68Ga-NeoBOMB1.