Registration of MR permeability and FDG uptake in pediatric brain tumors: A report from the Pediatric Brain Tumor Consortium (PBTC)

Objectives To develop a method of registering FDG PET with MR permeability images for investigating their correlation in pediatric brain tumors.

Methods Twenty-four children with brain tumors in a Phase II study of Bevacizumab + Irinotecan had both brain MR and FDG PET within 2 weeks. Tumor types included supratentorial high-grade astrocytoma (7), low-grade glioma (9), brainstem glioma (4), medulloblastoma (2) and ependymoma (2). There were 33 total cases (pre-treatment only (12), post-treatment only (3) and both pre- and post- treatment (9)). FDG PET images were registered to MR images from the last time point of the T1 perfusion time-series using mutual-information. 3D regions of interest (ROIs) drawn on permeability images were automatically transferred to registered PET images. Quality of ROI registration was graded on a 5 point scale (1-excellent, 2-very good, 3-good, 4-fair, 5-poor) by 3 independent experts. Cox Proportional Hazards Models were used to investigate associations of maximum tumor permeability (KPS) and maximum tumor FDG uptake normalized to white matter (T/WMax), with progression free survival (PFS).

Results The quality of registration between MR and PET was good to excellent in 31/33 cases. Over all brain tumors: 1. There was no correlation of KPS with T/WMax (Spearman’s Rank Correlation=0.07 (p=0.76)), 2. KPS was not significantly associated with PFS (p=0.43, Hazard Ratio=0.96, n=21, nevnts=14); 3. Although not significant, T/WMax suggested an association with PFS (p=0.10, Hazard Ratio=1.46, n=21, nevnts=14).

Conclusions MR permeability and FDG uptake were successfully registered and compared across a spectrum of pediatric brain tumors. A larger number of patients is needed for a covariate analysis of the two parameters and PFS by tumor histology