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BEST IN PHYSICS (JOINT IMAGING-THERAPY) - Assessment of Radiation-Induced White Matter Injury in Sub-Structures of Normal-Appearing Brainstem Using Diffusion Tensor Imaging

J Uh

J Uh*, T Merchant, R Ogg, C Hua, St. Jude Children's Research Hospital, Memphis, Tennessee

WE-C-BRA-2 Wednesday 10:30:00 AM - 12:30:00 PM Room: Ballroom A

Purpose: To test the hypothesis that treatment-induced white matter injury assessed by diffusion tensor imaging (DTI) is uniform across sub-regions of the normal appearing brainstem.

Methods: We analyzed serial DTI data, acquired before radiation/chemotherapy and over 4-6 years of follow-up, from 11 pediatric patients (age 5-16 years) with medulloblastoma. FSL4.1 software (FMRIB, Oxford, UK) was used to calculate fractional anisotropy (FA) and mean, axial, and radial diffusivities. For a consistent identification of regions of interest (ROIs), parametric maps of each patient were transformed to a standard brain space (ICBM), on which we identified motor (corticospinal tract, CST) and sensory (medial lemiscus, ML) tracts in the pons and transverse pontine fibers (TPF) involved in coordination. Temporal changes of DTI parameters in ROIs were evaluated using a linear mixed effect model.

Results: Therapy-induced white matter injury was marked by a decline in FA at 1-3 years after treatment. The decline was often accompanied by decreased axial diffusivity and/or increased radial diffusivity. This implied axonal damage and demyelination. We observed that the magnitude of the changes was not always uniform across sub-regions of the brainstem. Specifically, the changes in DTI parameters for TPF were more pronounced than in other regions (p<0.001 for FA) despite similarities in the distribution of dose. The mean dose to CST, TPF, and ML was 52.3, 56.0, and 56.6 Gy, respectively. We did not find a significant difference between CST and ML in these patients (p>0.08 for all parameters).

Conclusions: These results indicate that fiber tract sensitivity to radiation effect may be associated with the type and function of fiber tracts and support a role for tract-based assessment in radiation treatment planning and evaluation of treatment response.

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