Radiation-induced gray matter atrophy in patients with nasopharyngeal carcinoma after intensity modulated radiotherapy: a MRI magnetic resonance imaging voxel-based morphometry study

Abstract

Background: Gray matter (GM) damage after radiotherapy (RT) in nasopharyngeal carcinoma (NPC) patients can result in cognitive impairment, while there may be no visible brain tissue change according to the conventional magnetic resonance imaging (MRI). This study investigated radiation-induced GM volume differences between NPC patients who received RT and those who did not.

Methods: High-resolution brain structural MRI data from two groups of patients were acquired. The pre-RT group was composed of 56 newly diagnosed but not yet medically treated NPC patients, while the after-RT group consisted of 40 NPC patients who had completed RT more than 1 year ago. Voxel-based morphometry (VBM) was applied to assess GM volumes. Two sample t-test was used to analyze GM volumes voxel-by-voxel using the VBM8 toolbox built in the SPM software. Radiation-induced cortical volume alteration in all NPC patients after RT and dosimetry of 36 patients were analyzed.

Results: Compared to pre-treatment group, cortical volumes of GM were significantly smaller in the left hippocampus, the right pulvinar and the right middle temporal gyrus (MTG, P<0.001, AlphaSim correction, cluster size ≥157). The mean dose (D_mean) for bilateral hippocampal heads were significantly higher than other different parts of the brain (P<0.001). No significant correlations between the GM volume in any brain regions and the mean dose of corresponding position of these brain regions were observed (P>0.05).

Conclusions: Radiation to the NPC patients can not only induce damage of the hippocampus, but also other secondary damages of GM.

Keywords: Nasopharyngeal carcinoma (NPC); gray matter volume; magnetic resonance imaging (MRI); radiotherapy (RT).

Figure 1

Whole-brain MR (A) and MR axial images (B) of the significant clusters reveal gray matter volume decrease in NPC patients in the post-RT group compared to patients in the non-RT group (P<0.001, AlphaSim correction, minimum cluster size of 157 voxels). T-score bar is shown on the right. MR, magnetic resonance; NPC, nasopharyngeal carcinoma; RT, radiation therapy.

Figure 2

The comparison figure of brain tissue dose distribution and hippocampus atrophy in nasopharyngeal carcinoma treated with radiotherapy. (A) The dose distribution on CT images of the RT plan in the brain; (B) the location of the hippocampus on structural MRI; (C) the DVH of bilateral hippocampus head in the RT plan. The diagram of the exposed dose and the DVH indicates that both L.HH and R.HH were exposed to radiation. L.HH shows significant atrophy in the post-RT group. CT, computer-tomography; RT, radiation therapy; MRI, magnetic resonance; DVH, dose volume histogram; L.HH, left hippocampal head; R.HH, right hippocampal head; PGTV, planned gross tumor volume; PTV, planned target volume.

Figure 3

No significant difference in mean radiation dose was detected between L.HH and R.HH (P=0.99). D_mean for L.HH and R.HH are significantly higher than that for others (P<0.001). ROI, regions of interest; L.HH, left hippocampal head; R.HH, right hippocampal head; R.PV, right pulvinar; R.MTG, right middle temporal gyrus.