Radiation therapy (RT) induces vascular changes that increase the risk of cardiovascular diseases in some patients. The objective was to determine if in vivo positron emission tomography (PET) with fluorodeoxyglucose (¹⁸F-FDG) can identify increased vascular inflammation in patients without changes in vascular intima media thickness (IMT). Patients previously receiving unilateral RT due to lymphoma were prospectively recruited (N=10). The untreated contralateral artery functioned as control. All patients underwent a dedicated vascular PET/CT. Vascular tracer uptake was quantified by drawing regions of interests around the carotid artery or the iliac arteries. The IMT of the carotid arteries was measured using ultrasound. Eight patients (25% male, 42-83 years old) that had received RT involving unilateral carotid arteries and 2 patients (both male, 38 and 58 years old) that had received radiotherapy involving the unilateral iliac artery were included. The patients had completed their RT 2-7 years before. Eight patients showed increased uptake of ¹⁸F-FDG in the irradiated side compared to the non-irradiated side, 1 showed no difference, while 1 patient showed highest uptake in the non- irradiated side (P=0.04). Measurement of IMT showed that 4 patients had the highest thickness in the irradiated side, while the other 4 patients had the highest thickness in the non-irradiated side (P=0.8). In conclusion, we found that (18)F-FDG PET imaging may be used to detect vascular changes induced by RT. Larger prospective follow-up studies are needed to determine the prognostic value of increased vascular FDG-uptake.