Inactivated and mRNA COVID-19 Vaccines Affect 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Oncology Patients

Introduction: We aimed to analyse the effect of coronavirus disease 2019 (COVID-19) vaccination on F-18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) imaging findings in cancer patients. Methods: A total of 165 oncology patients who underwent FDG PET/CT between 1 May 2021 and 30 September 2021 after their first or second COVID-19 vaccination with were included in this retrospective study. The occurrence and pattern of FDG uptake at the injection site (usually deltoid), ipsilateral axillary and other regional lymph nodes, were measured. Results: Overall, the incidence of FDG-avid ipsilateral regional nodal uptake was 26.7% (44/165), with a median maximal standardised uptake value of 3.2 (range, 1.7-13.8). Vaccine-associated hypermetabolic lymphadenopathy (VAHL) was found in 11.4% (5/44) of the subjects beyond 6 weeks after vaccination. VAHL was more common in patients receiving BioNTech-Fosun mRNA vaccine (compared with patients receiving the Sinovac CoronaVac inactivated vaccine), and in women (p < 0.05). Conclusion: VAHL is common and can be observed beyond 6 weeks after vaccination. It was seen more frequently in women and in patients receiving the mRNA-based vaccine. Proper vaccination history documentation, locating the vaccination site contralateral to the primary cancer, and appropriate scheduling of FDG PET/CT are advisable for correct image interpretation.