Decreased brain FDG uptake in patients with FDG-avid non-Hodgkin lymphoma lesions

Objectives The purpose of this study was to investigate whether there was a correlation between massive tumor uptake and reduced brain uptake on FDG-PET/CT.

Methods Fifty non-diabetic patients(pts) having confirmed non-Hodgkin lymphoma with SUV of >10 who underwent FDG PET/CT between January and November 2008 were enrolled. Thirty age- and sex-matched non-diabetic control subjects were also included to evaluate normal brain uptake. PET/CT examinations were retrospectively reviewed. The threshold SUV of the volumetric regions of interest (VOI) on PET images was determined by referring to CT images, and average SUV (SUVavg) was measured. The products of SUVavg and tumor volume (SUVavg×cm³; amount of lymphoma uptake(ALU)) were calculated. In the pts having two or more lesions, ALU was defined as the sum of ALU of each lesion. The maximum SUV (SUVmax) and SUVavg were measured in the cerebrum and cerebellum. The values of ALU and brain FDG uptake were plotted and analyzed.

Results In the control subjects, SUVavg and SUVmax were 6.61±1.02 and 12.76±1.92 in the cerebrum, and 6.34±0.90 and 8.63±1.20 in the cerebellum. In the lymphoma pts, the ALU correlated negatively with the brain uptake, showing regression line of y=-3.03E-4x+5.91(r=-0.67,p<.001) for cerebrum (SUVavg), y=-5.19E-4x+11.2 (r=-0.57,p<.001) for cerebrum (SUVmax), y=-3.07E-4x+5.99 (r=-0.69,p<.001) for cerebellum (SUVavg), y=-3.97E-4x+8.04 (r=-0.63,p<.001) for cerebellum (SUVmax).

Conclusions The significant negative correlation was observed between ALU and brain uptake. There may be a competition between lymphoma lesions and brain tissue during the accumulation process, that is, blood input function in brain may drop due to massive tumor uptake.