Influence of metabolic tumor burden on reference tissues' standardized uptake values in 18F-FDG PET/CT sequential imaging

Background Extremely hypermetabolic neoplastic tissues have been hypothesized to act as a "sink" reducing the amount of radiopharmaceutical available for uptake in other tissues, i.e., superscan phenomenon, the purpose of the study is to correlate the percent of change of metabolic tumor burden (MTB) with the standardized uptake values (SUVs) in reference tissues (liver, blood pool, brain and muscles) in sequential F-18-FDG PET/CT studies after therapy for different response groups (progression, regression and resolution) in all patients and in lymphoma patients.Results In all patients: there was significant negative correlation between % of change in MTB with % of change of SUV in liver, blood pool, brain and muscles (p < 0.05). In progression group: there was significant negative correlation between % of change in MTB with % of change of SUV in liver and in muscles only. In regression group: there was no significant correlation in all organs. In lymphoma patients: there was significant negative correlation between % of change in MTB with % of change of SUV in liver, blood pool and brain but not in muscles.Conclusions MTB can potentially affect F-18-FDG biodistribution in reference organs, which has a negative impact on semiquantitative analysis during interpretation of sequential studies. In lymphoma patients, normalizing tumor FDG uptake can be done to muscles as a potential stable reference tissue given that all other factors that could alter biodistribution were considered.