Brain tumor imaging with PET and 2-[carbon-11]thymidine

To assess the potential of thymidine for imaging brain tumors, 20 patients with untreated (n = 14) and recurrent (n = 6) supratentorial intracranial tumors were studied with PET by using 2-[11C]thymidine (Tdr), and the results were compared with [18F]fluorodeoxyglucose (FDG) PET data.

Blood analysis consistently revealed a rapid clearance of the intact Tdr together with the appearance of CO2/HCO3- that, with time, accounted for approximately 70% of the total blood activity. As soon as 10 min after tracer injection, brain images showed a low and homogeneous Tdr distribution over the normal brain structures (cortex-to-blood ratio approximately 1). Visual and quantitative analysis revealed increased Tdr uptake (tumor-to-cortex ratio > or = 1.2) in 11 of 14 untreated tumors and in 5 of 6 recurrent tumors. No correlation was found between Tdr uptake and tumor grade. In 12 of the 14 untreated tumors, FDG uptake was low (tumor-to-cortex ratio: 0.83 +/- 0.79), but a FDG hot spot was visualized in 8 of 10 high-grade and in none of the 4 low-grade tumors. FDG uptake was consistently low in recurrent tumors (tumor-to-cortex ratio: 0.49 +/- 0.19), and PET-FDG was negative in 3 of the 6 cases.

These data indicate the feasibility of brain tumor imaging with Tdr and suggest the potential clinical usefulness of the method in the detection of tumor recurrences. The specificity of the method remains, however, to be investigated.