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目的：探讨鼻咽癌的合理照射体位及设野的剂量分布特点，比较几种体位固定方法的摆位重复性和位移情况。方法：利用 TPS探讨常规和改进体位下设野的合理性和剂量分布特点；将 120例鼻咽癌随机均分成砂袋组、面罩组、泡沫塑枕组和等距离照射（ SSD）组，利用模拟机模拟定位和治疗过程 ,并分别摄取头颅侧位片，测量各照片间中心点的移动距离。结果：改进体位和设野与常规设野比较靶区中心剂量差别不大，但明显提高了茎突后、后组筛窦和眶尖等靶区边缘的剂量，降低了脑干中、脊髓、口腔和下颌角区的剂量；各组间摆位重复性的差别无统计学意义，放疗过程中发生位移的例数 SSD组和砂袋组明显多于其它两组。结论：改进体位有利于合理布野，避免射野间的重叠，配合低熔点铅挡块技术，能使靶区剂量分布更均匀； SSD照射和砂袋固定法不宜继续使用，泡沫塑枕值得临床推广，面罩在改进后可继续使用。
Objective: To investigate the reasonable irradiation position of nasopharyngeal carcinoma (NPC) and its dose distribution characteristics, and to compare the placement repeatability and displacement of several fixed-position methods. Methods: TPS was used to investigate the rationality and dose distribution characteristics of routine and improved orthodontics. 120 cases of nasopharyngeal carcinoma were randomly divided into sand bag group, mask group, foam pillow group and SSD group. The simulator was used to simulate the positioning and treatment process, and the cranial flaps were taken respectively to measure the movement distance of the center points among the photos. Results: There was no significant difference in the central dose between the improved position and the open field compared with the conventional field, but significantly increased the dose at the edge of the ethmoid sinus and the orbital apex of the posterior segment of the styloid process, Mouth and mandibular angle of the dose; placement repeatability between the groups was not statistically significant, the number of cases of displacement during radiotherapy SSD group and sand bag group was significantly more than the other two groups. Conclusion: The improvement of body position is beneficial to the rational distribution of cloth and avoid the overlapping between the fields. With the technology of low melting point lead stopper, the dose distribution in the target area can be more uniform. SSD irradiation and sand bag fixation should not be used continuously. , The mask can be used after improvement.