Weifeng Xiong MD, Presenter: Nothing to Disclose

Shi Jun Qiu MD, Abstract Co-Author: Nothing to Disclose

To detect radiation-induced changes of temporal lobe normal-appearing white mater (NAWM) following radiation therapy (RT) for nasopharyngeal carcinoma (NPC)

Seventy-five MRS and DTI examinations were performed in 55 patients before and after a single irradiation (total dose; 66-75GY). We divided the dataset into 6 groups based on time after completion of RT: group 1 (pre-RT; n=18), group 2 (0-3 months; n=16), group 3 (>3-6 months; n=12), group 4 (>6-9 months; n=10), group 5 (>9-12 months, n=8), and group 6 (>12months; n=11). N-acetylaspartic acid (NAA)/choline (Cho), NAA/creatine (Cr), Cho/Cr, mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (λ⊥)and axial diffusivity(λ‖) were calculated in bilateral temporal lobe NAWM.

NAA/Cho and NAA/Cr decreased and λ⊥ increased significantly within 1 year after RT (groups 2-5) compared with pre-RT (group 1). In group 6, NAA/Cho, NAA/Cr, and λ⊥ were not significantly different from pre-RT. In all post-RT groups, FA decreased significantly. Variations over time were the same for NAA/Cho, NAA/Cr, and FA, and minimal values were found at 0-3 months and again at >9-12 months after RT. λ‖ decreased within 9 months after RT (groups 2-4) compared with pre-RT, but was not significantly different from pre-RT more than 9 months after RT (groups 5 and 6). The Cho/Cr ratio and MD values of in post-RT groups were not significantly different from those in the pre-RT group. Variations in both MD values and Radial diffusivity (λ⊥)  over time were similar.

   Metabolic alterations and water diffusion characteristics of temporal lobe NAWM in patients with NPC after RT were dynamic and transient. These changes may be due to irreversible injury of small partial neurons, blood-brain barrier disruption and repair, demyelination and remyelination, and axonal injury and repair processes.    The NAA/Cho, NAA/Cr, FA,  λ⊥ and λ‖ changes versus time were not the same due to differences in the speed with which myelin and axons were repaired. During the recovery period, may be attributed to an enlarged oligodendrocyte population, newly formed myelin sheaths around additional axons, and a gradual increase in axonal caliber. The sensitivity of MD is lower than that of FA.

We hope that our results will provide more evidence to facilitate clinical treatment decision-making and postpone the occurrence of radiation-induced encephalopathy.

Xiong, W, Qiu, S, ¹H-MR Spectroscopy and Diffusion Tensor Imaging of Normal-appearing Temporal White Matter in Patients with Nasopharyngeal Carcinoma after Irradiation: Initial Experience.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11007558.html