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

Mai A Elahmadawy, Moatasem El-Ayadi, Soha Ahmed, Amal Refaat, Magdy H Eltaoudy, Eslam Maher, Hala Taha, Mohamed Elbeltagy

F18-FET PET has an established diagnostic role in adult brain gliomas, here we analyzed image derived static & dynamic parameters with available conventional MRI, histological, clinical & follow up data in assessment of pediatric brain tumor patient at different stages of the disease. 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 & maximum Tumor to Brain Ratio "TBR" & Biological Tumor Volume "BTV") parameters evaluation as well as the Time Activity Curve "TAC". 19 out of 20 initially assessed patients had pathologically &/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 & late BTV & Event Free Survival "EFS" (P value =0.042 & 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 posttherapy 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 & residue/recurrence in post-therapy scans) with 80% sensitivity & 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). F18-FET PET seems to be an evolving pediatric neuroimaging technique with valuable diagnostic & prognostic information at initial and post-therapy evaluation.