Effect of the Maximum Dose on White Matter Fiber Bundles Using Longitudinal Diffusion Tensor Imaging.
Previous 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 to whole-brain white matter (WM) after partial-brain irradiation might also be important. Therefore, we carried out a study to develop the methodology to assess radiation therapy (RT)-induced damage to whole-brain WM bundles.



An 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 or benign brain tumors treated by RT. Six DTI scans per patient were performed from before RT to 18 months after 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 diffusivity (AD) and radial diffusivity (RD) from before RT.



Among 22 fiber bundles, AD or RD changes in 12 bundles were affected significantly by doses (P<.05), as the effect was progressive over time. In 9 elongated tracts, decreased AD or 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 after RT. The dose effect on WM was greater in older female patients than younger male patients.



Our study demonstrates for the first time that the maximum dose to the elongated WM bundles causes post-RT damage in WM. Validation and correlative studies are necessary to determine the ability and impact of sparing these bundles on preserving neurocognitive function after RT.
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
Tong
T
Zhu
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
Christopher H
CH
Chapman
Department of Radiation Oncology, Washington University at St Louis, St Louis, Missouri.
Christina
C
Tsien
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
Michelle
M
Kim
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
Daniel E
DE
Spratt
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
Theodore S
TS
Lawrence
Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan; Department of Radiology, University of Michigan, Ann Arbor, Michigan; Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan. Electronic address: yuecao@umich.edu.
Yue
Y
Cao
D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D066127:White Matter / Q000000981:diagnostic imaging / Q000473:pathology* / Q000528:radiation effects*; D014916:Whole-Body Irradiation / Q000009:adverse effects*
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