[11C]-L-Methionine positron emission tomography in the mManagement of children and young adults with brain tumors

Background: Methyl-[¹¹C]-L-methionine ([¹¹C]MET) positron emission tomography (PET) is a well established method in the diagnosis and management of adult patients with brain tumors. Only a few [¹¹C]MET-PET studies have focused on children with brain neoplasm. Because of the radiation exposure, long scan acquisition time, and the need for sedation in very young children [¹¹C]MET-PET studies should be restricted to children with brain tumors where a clear decision for further therapy management is not possible from magnetic resonance imaging (MRI) alone.

Purpose: We investigated the diagnostic accuracy of [¹¹C]MET-PET for the differentiation between tumor and non-tumorous lesions in this selected group of patients.

Patients and Methods: A total of 48 [¹¹C]MET-PET scans were performed in 39 patients aged 21 years or younger (mean age 15 years, range 2–21 years). 17 children were under the age of 15 years. In all patients a newly diagnosed (n=18) or recurrent (n=31) brain tumor was suspected on MRI. For analyses a circular ROI of 7mm diameter was placed in the area of maximum [¹¹C]MET-uptake. Within each ROI, mean uptake was determined relative to a corresponding contralateral control region or in midline or brainstem tumors to a frontolateral cortical region. To determine the relative [¹¹C]MET-uptake value that best distinguishes tumor from non-tumorous brain lesions, receiver operating characteristic (ROC) analysis was performed by varying the threshold of [¹¹C]MET-uptake over the whole range of values and calculating sensitivity and specificity for each value (see Figure).

Results: At a threshold of 1.37 relative [¹¹C]MET-uptake sensitivity was 86% and specificity 92%, respectively (area under the curve=0.95, 95% confidence intervall=0.89–1.00) for the differantiation between tumor (n=36) from non-tumorous brain lesions (n=12). A differentiation between malignant lesions (medulloblastoma, PNET and glioma WHO grade III and IV, mean [11C]MET-uptake=2.26±0.62) and more benign tumors (DNT, desmoplastic infantile ganglioglioma and glioma WHO grade I and II, mean [¹¹C]MET-uptake=1.97±0.62) was not possible.

Conclusion: [¹¹C]MET-PET is a very useful tool to differentiate tumor from non tumor lesions in selected children when a decision for further therapy management is difficult or impossible from MRI alone.

Fig. 1: ROC analysis of relative [¹¹C-MET]-uptake to differentiate tumor from non-tumotous lesions.