Effect of the Maximum Dose on White Matter Fiber Bundles Utilizing Longitudinal Diffusion Tensor Imaging

Publication date: Available online 21 July 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Tong Zhu, Christopher H. Chapman, Christina Tsien, Michelle Kim, Daniel E. Spratt, Theodore S. Lawrence, Yue Cao
PurposePrevious efforts to decrease neurocognitive effects of radiation focused on sparing isolated cortical structures. We hypothesize that understanding temporal, spatial and dosimetric patterns of radiation damage of whole brain white matter (WBWM) after partial brain irradiation might also be important. Therefore, we carried out a study to develop the methodology to assess radiotherapy-induced damage to WBWM bundles.MethodsAn atlas-based, automated WM tractography analysis was implemented to quantify longitudinal changes in indices of diffusion tensor imaging (DTI) of 22 major WM fibers in 33 patients with predominantly low-grade/benign brain tumors treated by radiotherapy. Six DTI scans per patient were performed from pre-RT to 18 months post-RT. The DTI indices and planned doses (maximum and mean doses) were mapped onto profiles of each of 22 WM bundles. A multivariate linear regression was performed to determine the main dose effect as well as the influence of other clinical factors on longitudinal percentage changes in axial and radial diffusivity (AD and RD) from pre-RT.ResultsOf 22 fiber bundles, AD/RD changes in 12 bundles were affected significantly by doses (P<0.05), as the effect was progressive over time. In nine elongated tracts, decreased AD/RD was significantly related to maximum doses received, consistent with a serial-structure. In individual bundles, AD changes were up to 11.5% at the maximum dose locations 18 months post-RT. The dose effect on WM was greater in older females than younger males.ConclusionOur study demonstrates for the first time that the maximum dose to the elongated WM bundles causes post-radiotherapy damage in WM. Validation and correlative studies are necessary to determine the ability and impact of sparing these bundles on preserving neurocognitive function post-radiotherapy.

Teaser

Neurocognitive function is supported by white matter (WM) fiber bundles in the neural network. WM bundles are highly susceptible to radiation damage. In this study, we found that elongated WM fiber bundles responded to the received maximum dose rather than the mean dose, much like a typical serial-structure. These findings provide a new framework on how to spare dose for critical functional networks to preserve cognitive function.


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