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目的:利用在线采集的千伏级锥形束CT(cone beam computed tomo-graphy,CBCT)图像,分析鼻咽癌放疗过程中摆位误差的大小,从而获得临床靶区(clinical target volume,CTV)的合理外放边界。方法:16例鼻咽癌患者均采用三维适形放疗或调强放疗。放疗过程中以传统的热塑面膜固定头颈部,激光灯摆位。分次放疗前患者在治疗床上进行CBCT扫描,并将CBCT图像与计划CT图像进行在线配准,根据配准得到的平移矢量调整治疗床的位置,从而修正摆位误差,并分别记录各个方向上平移矢量。结果:16例患者共计160组配准数据。为满足至少95%放疗分次的CTV接受处方剂量,计划靶区各方向上的外放间距均为4 mm。结论:鼻咽癌三维适形调强放疗时具有一定的摆位误差。基于千伏级CBCT图像分析的在线校正方法能减小该摆位误差,并有助于确定合适的CTV外放。
OBJECTIVE: To analyze the setting error of nasopharyngeal carcinoma (NPC) during radiotherapy by using a cone beam computed tomo-graphy (CBCT) image acquired online to obtain the clinical target volume (CTV) Reasonable extrinsic boundary. Methods: 16 cases of nasopharyngeal carcinoma patients were treated with three-dimensional conformal radiotherapy or intensity-modulated radiation therapy. Radiation therapy to the traditional thermoplastic mask fixed head and neck, laser light position. Patients were divided into groups before radiotherapy CBCT scan on the treatment bed, and CBCT images and planned CT images online registration, based on the registration of the translation vector to adjust the position of the treatment bed, so as to correct the setup error, and were recorded in all directions Panning vector. Results: A total of 160 patients with 16 sets of registration data. To meet the prescription dose of at least 95% of the radiotherapy fraction of CTV, the planned target area in all directions are 4 mm. Conclusion: Three-dimensional conformal intensity modulated radiotherapy for NPC has some errors. The online calibration method based on KV CBCT image analysis can reduce the setup error and help to determine the proper CTV placement.