F18-FET PET in pediatric brain tumors: integrative analysis of image derived parameters and clinico-pathological data.

Background: F18-FET PET has an established diagnostic role in adult brain gliomas. In this study we analyzed image derived static and dynamic parameters with available conventional MRI, histological, clinical and follow-up data in assessment of pediatric brain tumor patients at different stages of the disease.

Methods: Forty-four pediatric patients with median age 7 years, diagnosed with brain tumors and underwent forty-seven 18F-FET PET scans either initially (20 scans) or post-therapy (27 scans) were enrolled. Standardized analysis of summed FET PET images early from 10-20 min and late from 30-40 min post-injection were used for static (mean and maximum tumor to brain ratio [TBR] and biological tumor volume [BTV]) parameters evaluation as well as the time activity curve [TAC].

Results: Nineteen out of 20 initially assessed patients had pathologically and/or clinico-radiologically proven neoplastic lesions and one patient had pathologically proven abscess. Receiver operator curve (ROC) marked early TBR max 2.95, early TBR mean 1.76, late TBR max 2.5 and late TBR mean 1.74 as discriminator points with diagnostic accuracy reaching 90% when TBR max was combined with dynamic parameters. Significant association was found between initial FET scans, early and late BTV and event free survival (EFS) (P value=0.042 and 0.005 respectively). In post-therapy assessment, the diagnostic accuracy of conventional MRI was 81.48% when used alone and 96.30% when combined with F18-FET PET scan findings. A cutoff point of 3.2 cm³ for late BTV, in post-therapy scans, was successfully marked as a predictor for therapy response (P value 0.042) and was significantly associated with EFS (P value 0.002). In FET-avid / MRI non-enhancing lesions, early TBR max was able to detect highly malignant processes (high-grade tumors in initial scans and residue/recurrence in post-therapy scans) with 80% sensitivity and 100% specificity when cutoff value of 2.25 was used (P value=0.024). In patients with FET-avid brainstem lesions, whether enhancing or non-enhancing in MRI scans, 81.8% were associated with high risk diagnoses and 68.2% of them were associated with poor therapy outcome. The degree of FET uptake matched tumor-grading, but did not show significant association with OS or EFS (P value>0.05).

Conclusions: F18-FET PET seems to be an evolving pediatric neuro-imaging technique with valuable diagnostic and prognostic information at initial and post-therapy evaluation.