Initial study of FDG PET for pediatric non-Hodgkin lymphoma (NHL) treatment response assessment

Objectives There is limited published data and no systematic review of utilization of FDG PET/CT for treatment response in pediatric NHL. We evaluated the utility of the current IWG criteria for lymphoma assessment using mediastinal blood as reference standard for pediatric NHL post-therapy and surveillance response.

Methods Retrospective analysis of 10 pediatric NHL patients in a single institution, of whom five patients had 3 to 4 year clinical long term follow-up (LFU). A total of 47 available FDG PET/CT at baseline, post-therapy, and/or surveillance periods were analyzed. Visual assessment on five-point scale (1=no activity, 2=less than blood pool, 3=between blood pool and/or equal to liver, 4=moderately above liver, 5=significantly more than liver). Tumor types includes 4 Burkitts, 2 large B-cell, T-cell anaplastic, marginal zone B-cell, primary B-cell mediastinal, B-cell lymphoblastic lymphomas.

Results A total of 23 sites of FDG avid disease including lymph nodes, bone/bone marrow, bowel, tonsils, salivary gland, and sinuses were identified. There were 17 sites with visual score of 3 or higher on post-therapy or surveillance scans (higher than blood pool), with 1 true-positive (TP) and 11 false-positive (FP) seen on those with LFU. Most of these FP sites were in non-nodal sites (tonsil, scalp, bone/marrow, and bowel). Six sites had visual score of 1 or 2 (less than blood pool), with 2 true-negative on LFU.

Conclusions Preliminary assessment of FDG PET visual assessment in pediatric NHL demonstrated a high FP rate, especially at sites of non-nodal disease due to high background or native organ FDG activity. Current FDG PET visual criteria for lymphoma assessment based on blood pool reference is likely insufficient for evaluation of pediatric NHL treatment response