Lymphoma Therapy Response Assessment with Low-Dose [¹⁸F]FDG Total-Body PET/CT.

Area of Science:

• Nuclear Medicine
• Oncology
• Radiochemistry

Background:

• Total-body (TB) PET/CT offers enhanced sensitivity, enabling potential reductions in injected radiotracer activity.
• Optimizing injected doses is crucial for patient safety and cost-effectiveness in routine clinical practice.

Purpose of the Study:

• To determine the lower limit of reduced injected [18F]FDG activity for interim and end-of-treatment assessment in lymphoma patients using TB PET/CT.
• To evaluate the impact of dose reduction on quantitative imaging parameters and therapy response assessment.

Main Methods:

• Prospective enrollment of 24 lymphoma patients undergoing interim and end-of-treatment TB PET/CT.
• Simulated reduced [18F]FDG activities (1.0 to 0.125 MBq/kg) from a reference standard (3.0 MBq/kg) acquired at 1 and 2 hours post-injection.
• Analysis of SUV, liver coefficient of variation, metabolic tumor volume (MTV), total-lesion glycolysis (TLG), tumor-to-background ratios (TBRs), contrast-to-noise ratios, and Deauville criteria for therapy response.

Main Results:

• SUVmax showed a trend towards increase with reduced activity, but MTV and TLG remained comparable to the reference standard.
• Liver coefficient of variation increased significantly with decreasing activity, while TBRs showed minimal significant changes.
• Deauville scores remained comparable to the reference standard down to 0.25 MBq/kg at 1h and 1.0 MBq/kg at 2h post-injection.

Conclusions:

• Injected [18F]FDG activity can be reduced in TB PET/CT for lymphoma therapy response assessment without significantly impacting MTV, TBR, or TLG.
• SUVmax and Deauville scores remain reliable indicators of response within specific reduced dose limits (0.25 MBq/kg at 1h, 1.0 MBq/kg at 2h).
• These findings support dose optimization strategies for [18F]FDG TB PET/CT in lymphoma management.