RA-12: ASSESSMENT OF CHANGES IN STRUCTURAL CONNECTIVITY OF THE CENTRAL EXECUTIVE NETWORK DURING CRANIAL RADIOTHERAPY IN CHILDREN TREATED FOR MEDULLOBLASTOMA

To understand the association between cranial radiation therapy (CRT) and neurocognitive deficits, this study assesses changes in structural connectivity of the central executive network (CEN) in response to CRT. Thirty medulloblastoma patients (Age at exam 11.2 + 5.2 years; 8 average-risk [23.4 Gy CRT], 22 high-risk [36.0 Gy CRT]) were imaged Pre- and Post-CRT using 30 direction diffusion tensor imaging (DTI) with 1.8x1.8x2.0 mm spatial resolution. Probabilistic tractography was performed between the 20 brain structures (4 sub-cortical and 6 cortical for each hemisphere) included in the CEN with 500 permutations from each node. Differences in metrics were tested using a paired T-test. Associations between imaging and neurocognitive measures of working memory, executive function, and reaction time (CogState battery, N = 13) were tested using a multiple linear regression model with age as a covariate. Significant drops in fractional anisotropy (FA) and axial diffusivity (AX) were demonstrated bilaterally in almost all CEN subnetworks after irradiation (P-values < 0.03). No significant differences between the risk arms were demonstrated for this small unbalanced sample. There was some evidence of an association between DTI and neurocognitive measures but these were limited by the small sample size and potential outliers. Additional investigation of associations with neurocognitive performance at 12 months post diagnosis is planned with a larger subset. Decreased FA and AX suggests a significant reduction in microstructural integrity within the CEN immediately following irradiation. These findings support the use of the CEN model for evaluating changes early in therapy which could potentially be associated with later neurocognitive deficits.