鼻咽癌放疗后早期脑白质微观损伤DTI观察及其与受量关系研究

The microdamage of"morphologically normal white matter"in patients with nasopharyngeal carcinoma after radiotherapy and its correlation with the irradiation dose

目的探讨鼻咽癌患者放疗结束早期脑白质微观损伤情况及其与受量关系。方法33例鼻咽癌初诊患者分别在放疗前1周内,放疗结束后第1天行磁共振弥散张量成像(DTI)扫描和神经认知量表测试。采用基于全脑体素的分析方法计算部分各项异性(FA)、平均扩散率(MD)、平行本征值(λ‖)、垂直本征值(λ⊥),并将放疗前后的各组数据行配对t检验。亚组分析采用等分法,按照被试受照的颞叶平均剂量不同等分为3个组,组与组之间有相同剂量间隔,比较不同剂量组照射前后全脑变化情况,所有统计学结果均进行FDR校正。结果鼻咽癌患者放疗结束后全脑多个脑区FA、MD、λ‖、λ⊥值均有显著改变(P<0.05),发生显著改变脑区FA、MD、λ‖、λ⊥值分别为0.455±0.016、(9.893±0.403)×10^-4、(13.441±0.412)×10^-4、(8.231±0.429)×10^-4。亚组分析结果显示λ‖、λ⊥值随颞叶剂量增加,放疗后发生改变范围和程度增加,尤其高剂量组(平均剂量为25~35 Gy组)发生显著改变的范围较中剂量组(15~25 Gy)和低剂量组(5~15 Gy)扩大(P<0.05)。结论鼻咽癌患者刚刚放疗结束时,借助DTI技术可以在早期观察到脑白质的微损伤。颞叶所受的平均剂量的高低可能是影响这些微损伤程度的原因之一。未来或许可以借助此类成像技术寻求更精确的危及器官安全剂量阈值,也可以在放疗结束早期评估脑损伤高风险人群,最大限度地保护正常组织。

Objective To explore the correlation between microdamage in white matter and radiotherapy dose at early stage after radiotherapy(RT)in patients with nasopharyngeal carcinoma(NPC).Methods Thirty-three patients who were initially diagnosed with NPC were recruited and received diffusion tensor imaging(DTI)scan and neuro-cognitive scale test within 1 week before RT and the first day after RT.DTI-related characteristic parameters including fractional anisotropy(FA),mean diffusivity(MD),axial diffusivity(λ‖),and radial diffusivity(λ⊥)were calculated based on whole-brain voxel analysis method.Paired t-test was conducted to evaluate statistical significance between pre-RT and post-RT groups.In the subgroup analysis,all the subjects were divided into 3 groups according to the average dose of temporal lobe,and each group was set with an equal dose interval range.The DTI-related parameters of whole brain pre-RT and post-RT in each group were statistically compared.All the statistical results were corrected by FDR with a threshold of P<0.05 and clusters>100.Results FA,MD,λ‖andλ⊥in the post-RT group significantly differed compared with those in the pre-RT group(P<0.05).The values of FA,MD,λ‖andλ⊥were 0.455±0.016,(9.893±0.403)×10^-4,(13.441±0.412)×10^-4 and(8.231±0.429)×10^-4,respectively.Subgroup analysis showed that the extent and degree ofλ‖andλ⊥changes were exacerbated with the increase of the average dose of temporal lobe after RT.Particularly in high-dose group,the average dose range was 25-35 Gy and the extent of regions with significant changes was significantly larger than those in the medium-dose(15-25 Gy)and low-dose groups(5-15 Gy)(P<0.05).Conclusions DTI can be utilized to detect"normal"brain tissue microdamage in NPC patients at early stage after RT.The average radiation dose of temporal lobe may be one of the reasons for the severity of cerebral microdamage.In the future,DTI technique may be useful for guiding exposure dose of organs at risk during RT planning and to evaluate the cohort with a high risk of cerebral microdamage at early stage after RT,thereby protecting normal cerebral tissues to the maximum extent.