[18F]3'-deoxy-3'-fluorothymidine PET for the diagnosis and grading of brain tumors

The aim of this study was to evaluate the feasibility of using [(18)F] 3'-deoxy-3'-fluorothymidine (FLT) positron emission tomography (PET) for the diagnosis and grading of brain tumors.

The patient population comprised 26 patients (15 males, 11 females) with brain tumors (n=18) or nontumorous lesions (n=8). 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) and FLT PET images were obtained using a dedicated PET scanner 1 h after the injection of 370 MBq of FDG or FLT. Uptake of FDG and FLT by the lesions was visually and semiquantitatively assessed in comparison with normal brain tissue.

Of 26 brain lesions, four showed increased FDG uptake compared with normal gray matter (grade 5). These four lesions showed intensely increased FLT uptake and were all high-grade tumors. Twenty-two lesions with similar (grade 4) or decreased (grades 1-3) FDG uptake compared with normal gray matter showed variable pathology. Among the 18 brain tumors, FLT PET showed increased uptake in all 12 high-grade tumors but FDG uptake was variable. In 22 brain lesions with similar or decreased uptake compared with normal gray matter on FDG PET, the sensitivity and specificity of FLT PET for the diagnosis of brain tumor were 79% (11/14) and 63% (5/8), respectively. The uptake ratios of 14 brain tumors on FLT PET were significantly higher than the lesion to gray matter ratios (p=0.012) and lesion to white matter ratios (p=0.036) of FDG uptake and differed significantly between high (5.1+/-2.6) and low (2.1+/-1.1) grade tumors (p=0.029). In nine gliomas, FLT uptake was significantly correlated with the Ki-67 proliferation index (rho=0.817, p=0.007).

These findings indicate that FLT PET is useful for evaluating tumor grade and cellular proliferation in brain tumors. It displayed high sensitivity and good contrast in evaluating brain lesions that showed similar or decreased uptake compared with normal gray matter on FDG PET. FLT PET, however, did not appear to be sufficiently useful for differentiating tumors from nontumorous lesions.