Positron Emission Tomography and Computed Tomography in Differential Diagnosis between Recurrent or Residual Glioma and Treatment-Induced Brain Lesions

In previous studies of supratentorial gliomas with positron emission tomography (PET) and computed tomography (CT), high uptakes of L-methyl-¹¹C-methionine (¹¹C-L-methionine) were found even in astrocytomas without blood-brain barrier defects as judged by CT or ⁶⁸Ga-EDTA PET. In a number of patients examined after radiation therapy, there were no consistent changes in the high uptake values. In the present investigation PET and CT were compared with regard to their abilities to visualize and delineate recurrent tumors and treatment-induced brain defects and to differentiate between them. The study was undertaken on four patients who were long-term survivors after treatment for high-grade gliomas. For PET, ¹¹C-L-methionine and ⁶⁸Ga-EDTA were used. In two patients recurrent/residual tumors appeared considerably larger with ¹¹C-L-methionine PET than with CT or ⁶⁸Ga-EDTA PET. In one patient, no signs of recurrence were seen with any of these three methods, and in a fourth patient, whose condition was clinically stable, the findings at PET with ¹¹C-L-methionine were non-specific. In areas corresponding to the surgical parenchymal defects, the ¹¹C-L-methionine uptake and, except in one case, the local blood volume was markedly reduced. PET with ¹¹C-L-methionine thus has a potential for distinguishing between postoperative brain lesions and tumor recurrence with a higher accuracy than CT.