目的：通过对CT共轨系统获得的CT图像进行分析，量化鼻咽癌患者调强放疗分次治疗过程中的解剖结构变化，如原发肿瘤或淋巴结肿块的缩小、水肿区及整体体重的变化等，以期为临床治疗计划的重新设计提供依据。方法选取16例经病理诊断为鼻咽癌，原发病灶或肿大淋巴结最大直径≥4cm，接受调强放疗的患者；所有患者于整个治疗期间在CT共轨系统上接受每周3次，各次治疗体位相同的日常验证CT；在每层图像上重新手动勾画大体肿瘤靶区（GTV）和正常组织，分析所有患者分次治疗过程中解剖结构的变化。结果GTV在整个治疗期间以平均0.22 cm3/d的速率发生退缩，与原体积相比平均每天退缩2.06%；最后一次治疗结束时，GTV对比原病灶平均缩小了68.12%。腮腺体积也以平均0.10 cm3/d的速率发生退缩。结论在鼻咽癌调强放疗分次治疗期间，患者的解剖结构会发生明显的变化，GTV及危及器官体积、位置的变化在治疗3～4周后尤为明显，可能会导致高度适形治疗计划中各组织实际受照剂量与原治疗计划产生较大偏差。临床上应注重寻求调强放疗分次治疗过程中的解剖结构变化的规律，以利于开展自适应放疗，最大程度地提高治疗增益比。%Objective This paper was intended to quantify the anatomic changes in NPC (Nasopharyngeal Carcinoma) patients during their IMRT (Intensity Modulation Radiated Therapy) through analysis of CT images acquired by the CT-on-rail system, including shrinkage of the primary tumor, lymphatic nodal masses as well as changes in the edema area and weight, so as to provide the basis for re-design of clinical treatment plans. Methods Sixteen pathologically-conifrmed NPC patients whose primary lesions or lymphatic nodes were ≥4 cm in maximal diameter were enrolled in this pilot study. All the eligible patients were treated with IMRT and the CT-on-rail system thrice a week during the entire course of IMRT, which allowed for veriifcation of CT images in patients with the same position in each radiotherapy session. Both gross tumor volumes (GTV) and normal tissues were manually contoured on every axial slice. Results Shrinkage of GTV occurred at the mean speed of 0.22 cm3/d throughout the course of IMRT, which meant 2.06%shrinkage per day in comparison with the original volumes. On the last day of treatment, the GTV averagely shrunk 68.12%of the original one;while, the volume of parotid glands also degraded at the mean speed of 0.10 cm3/d. Conclusion Patients with NPC may experience anatomic changes throughout the course of IMRT. Changes in GTV as well as the volume and position of the affected organ became even more obvious especially in 3 to 4 weeks post-treatment and could result in large deviation between the actual radiation dose used in adaptive radiotherapy for each organ and that in the initial treatment plan. The regularity of anatomic changes during IMRT should be taken into account, which was convenient to deploy the adaptive radiotherapy and maximize the therapeutic ratio.
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