In Lugano staging, which imaging modality is used for response assessment?

• A. PET-CT
• B. CT alone
• C. MRI
• D. Ultrasound

Answer: (A)

Functional imaging with 18F-FDG PET-CT is used for response assessment in Lugano staging because it shows the metabolic activity of lymphoma lesions, not just their size. After therapy, metabolic change often precedes physical shrinkage, so PET-CT can indicate whether disease is still active (partial or no metabolic response) or has resolved metabolically (complete metabolic response). This makes response evaluation more accurate than relying on anatomy alone. The Lugano criteria, often using the Deauville five-point scale, depend on PET-CT findings to categorize response. CT alone lacks this functional information and may misclassify residual masses that are inactive; MRI is not practical for whole-body response in most lymphomas, and ultrasound cannot reliably assess deep nodal or visceral disease. Therefore, PET-CT is the best modality for response assessment.