| Purpose:To investigate the longitudinal volume changes in brain grey matter in nasopharyngeal carcinoma patients early after radiotherapy using whole brain three-dimensional structural MRI.The dynamic volume changes in whole grey matter,cortex of each brain region,ventricle,hippocampus and hippocampal subfields were analyzed.The correlation of volume changes and radiation dosage、MoCA scores were examined.The purpose of our study was to reveal the pattern of gray matter volume injury early after radiotherapy in nasopharyngeal carcinoma patients and provide objective imaging markers for the early clinical detection of brain gray matter volume injury.Materials and Methods:1.Subjects:The newly diagnosed patients with nasopharyngeal non-keratinized squamous cell carcinoma were selected by pathological biopsy.Three longitudinal follow-up evaluations were conducted in the NPC group(n=16)before,3 months after and 6 months after radiotherapy.Normal subjects with matching sex,age and education level were selected as the baseline control group(n=19).2.Data collection and cognitive evaluation:MRI data was acquired using a US GE Discovery MR 750 3.0 Tesla scanner.Each subject performed routine MRI sequence(T2WI,T1WI,T2 Flair)imaging scans,and performed high-resolution three-dimensional MRI imaging(3D-BRAVO)sequence.Neurocognitive function assessment was performed using the Beijing version of the Montreal Cognitive Assessment Scale(MoCA).3.Data processing:Structural images were processed using the FreeSurfer magnetic resonance data processing software(version 6.0).Gray matter volume of subjects was measured automatically and standardized,the hippocampal subfields were segmented by automatic algorithm.Specialized longitudinal processing process was used to analysis the brain structure data of NPC groups at 3 time points.4.Statistical analysis:SPSS 23 statistical software package was used to analyze the data.Independent sample T test was used to compare the MoCA scores and the volume parameters of each brain region in NPC group before radiotherapy and the NC group at baseline.Paired sample T test was used to compare the differences of MoCA scores within NPC groups.Single factor repeated measurement ANOVA was used to compare the differences of volume parameters at three times in NPC group,P<0.05 indicates statistically significant.The brain regions with statistically different volume changes were further pairwise compared within NPC group,P<0.0167 indicates statistically significant by using Bonferroni correction.Pearson Correlation Coefficient was used to analyze the correlation between the volume differences and the MoCA score differences at the same time after radiotherapy,and the radiation dosage of ipsilateral brain region,P<0.05 indicates statistically significant.Result:1.MoCA scores of NPC group at 3 and 6 months after radiotherapy were lower than that before radiotherapy(P<0.05).2.The volumes of total gray matter,bilateral frontal lobe,bilateral temporal lobe,bilateral parietal lobe,left occipital lobe,bilateral total hippocampus,bilateral subiculum,bilateral CA1 and CA 2/3,right CA4,right presubiculum,right parasubiculum,bilateral molecular layer,bilateral dentate granule cell layer,bilateral fimbria volume decreased with time,the ventricular volume increased with time(P<0.05);the total gray matter,ventricle,bilateral frontal lobe,bilateral temporal lobe,bilateral parietal lobe,bilateral total hippocampus,bilateral subiculum,bilateral CA1 and CA 2/3,right CA4,right parasubiculum,bilateral molecular layer,bilateral dentate granule cell layer,right fimbria showed dynamic changes in volume at different time points within NPC group(P<0.0167).3.Compared with NPC group before radiotherapy,the volume differences at NPC group 6 months after radiotherapy in the left hippocampal subiculum,left CA1,bilateral molecular layer,right granule cell layer,right total hippocam,pus were significantly positively correlated with the maximum/mean radiation dosage of the ipsilateral hippocampus;the volume differences in right subiculum 3 months after radiotherapy were significantly positively correlated with the maximum/mean radiation dosage of the right hippocampus(P<0.05,respectively).4.There was a significant positive correlation between the volume difference of the right hippocampus in NPC group 3 months after radiotherapy and the MoCA score difference 3 months after radiotherapy.(r=0.626,P =0.039).Conclusion:The gray matter volumes in multiple brain regions and hippocampal subfields decreased in the early stage after radiotherapy,revealing the early injury of gray matter structure in nasopharyngeal carcinoma patients after radiotherapy.The hippocampus and several subfields showed dose-dependent atrophy,and the volume damage in the right hippocampus tail was related to the cognitive function decline,suggesting that the hippocampus should be protected during the design of clinical target area to reduce the radiation damage.The results of this study showed that 3D-MRI structural imaging could detect the damage of brain gray matter structure in NPC patients after radiotherapy at an early stage. |
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