Vaccine-Related Lymph Nodes: The Emerging Pitfalls of 18F-Fluorocholine and 68Ga-PSMA-11 PET/CT in the Era of COVID-19 Vaccination.

PURPOSE

Vaccination against coronavirus disease 2019 (COVID-19) is currently under worldwide deployment. The consequences of this vaccination can be seen in radiology and nuclear medicine explorations with visualization of axillary lymph nodes (LNs), as observed on ultrasonography, MRI, or 18F-FDG PET/CT.We aimed to evaluate on PET/CT the incidence of vaccine-related LNs and their characteristics after COVID-19 vaccination, using several radiopharmaceuticals different from 18F-FDG.

PATIENTS AND METHODS

Between February and July 2021, all consecutive patients undergoing a whole-body PET/CT for any indication using a different radiopharmaceutical from 18F-FDG were eligible for inclusion if they had received at least 1 dose of the COVID-19 vaccine. The radiopharmaceutical administered and vaccine type were recorded for each patient. The incidence of positive vaccine-related axillary and supraclavicular LNs on PET/CT was our primary finding, along with the nodes characteristics. Statistical analyses were performed for patients with prostate cancer (PCa) to determine certain interaction factors that were associated with the detection of vaccine-related LNs.

RESULTS

Of the 226 patients in our cohort study, 120 patients underwent an 18F-fluorocholine PET/CT, 79 a 68Ga-PSMA-11 PET/CT, 6 an 18F-FDOPA PET/CT, and 21 a 68Ga-DOTATOC PET/CT. A total of 67.3% of patients (152/226) received BNT162b2mRNA (Pfizer-BioNTech), 26.5% (60/226) ChAdOx1-S (AstraZeneca), 4.9% (11/226) mRNA-1273 (Moderna), and 1.3% (3/226) Ad26.COV2.S (Janssen). The incidence of positive vaccine-related axillary and supraclavicular LNs was 42.5% (51/120 patients) on PET/CT using 18F-fluorocholine and 12.7% (10/79 patients) with 68Ga-PSMA-11. None of our patients undergoing 18F-FDOPA or 68Ga-DOTATOC PET/CT presented any vaccine-related lymphadenopathy. Vaccine-related LNs were statistically associated with the nature of the radiopharmaceutical (P < 10-4), with the number of vaccine doses received (P = 0.041), with a short delay between vaccination and PET/CT realization (P < 10-5), and with a higher prostate-specific antigen level for patients with PCa (P = 0.032), but not with age or vaccine type. The vaccine-related nodes appeared in 85% of the cases, in the 30 days after vaccine injection, were limited in size and uptake, and were most often limited to the axilla level 1 area.

CONCLUSIONS

Detecting positive LNs after COVID-19 vaccination is not an exclusive 18F-FDG PET/CT pattern but is common on 18F-fluorocholine and possible on 68Ga-PSMA-11 PET/CT. Confronting PET/CT findings with clinical data (such as date and site of injection) seems essential in the current pandemic context, just as it does for the radiopharmaceuticals used in PCa to avoid PET/CT misinterpretation and incorrect patient treatment. For 18F-FDOPA or 68Ga-DOTATOC PET/CT, this seems to have a lesser impact.