目的:分析鼻咽癌调强放疗过程中患者解剖结构的改变及其导致的剂量分布结果变化.方法:选取12例进行调强放疗的鼻咽癌患者,在完成25次治疗后重新进行CT扫描,重新勾画靶区和危及器官,并计算原计划在新CT上的剂量分布结果,分析靶区和危及器官的体积变化及剂量分布变化.结果:患者外轮廓的体积变化显著,变化率为-5.46％±2.66％,P＜0.05,左右腮腺的体积变化明显,分别达到-23.63％±12.30％和-25.51％±10.07％,GTV/CTV、脑干和下颌骨的体积没有显著变化.靶区的剂量分布情况无显著改变,PGTV的D95％和Dmean均无明显改变,脊髓和脑干的D0.1cc和D1cc均升高且超出正常限量范围,变化率分别达到12.66％、7.81％、13.77％和14.09％,左右腮腺的剂量均值显著升高,下颌骨的平均剂量和最大剂量数值无明显的变化,V50指数有明显的升高.结论:放疗过程中患者解剖结构的变化会导致危及器官的受量情况与原始计划产生较大偏差,因此对解剖结构变化大的患者重新进行CT扫描,重新勾画靶区和危及器官,重新进行计划设计和优化是十分必要的.%Objective:To analyze anatomical changes and dose distribution deviation of patients with nasopharyngeal carcinoma during intensity-modulated radiotherapy.Methods:Twelve NPC patients received intensity-modulated radiotherapy were selected to acquire second CT scan after 25 treatment fractions,targets and organ at risk were re-contoured,then computed the dose distribution on second CT scans with original beams arrangements,at last analyzed the anatomical changes and dose distribution deviation.Results:The volume of patient outlines decreased significantly by-5.46％±2.66％,P＜0.05,the volume of left and right parotids also decreased significantly by-23.63％ ± 12.30％ and-25.51％± 10.07％ respectively,but the volume of GTV/CTV,brainstem and mandible did not change much.The dose distribution of target changed slightly,the parameters D95％ and Dmean of PGTV kept stable,but the parameters D0.1cc and D1cc of spinal cord and brainstem increased significantly with increasing ratio of 12.66％,7.81％,13.77％ and 14.09％ respectively.The mean dose of bilateral parotids and mandible did not change much,but the V50 of mandible increased significantly.Conclusions:The dose distribution of organ at risk varies a lot comparing with the original treatment plan due to the patient anatomical changes during radiation treatment.So it's necessary to acquire re-scanning CT,re-contour target and OAR,re-design treatment plans for the patients with significant anatomical changes during radiotherapy.
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