鼻咽癌调强放疗靶区安全外扩边界研究

目的:利用电子射野影像验证系统(electronic portal imaging device,EPID)监测鼻咽癌调强放疗的摆位误差为PTV外扩边界提供依据,使得放射治疗计划的设计更为科学合理.方法:随机选取50例鼻咽癌调强放疗患者,采用“盲拍”模式获取患者治疗前及每周的摆位误差结果,根据公式MPTV =2.5∑ +0.7σ计算CTV到PTV外扩边界.结果:在左右、上下和前后各方向的误差分别为(0.0046±0.0875) cm,(0.048 3±0.065 1)cm和(0.027 2±0.137 3)cm;得到左右、上下和前后方向上外扩的边界分别为0.1 cm、0.4 cm、和0.4 cm.结论:通过图像引导方式监测患者的摆位误差情况,可以评估靶区安全的外扩边界.为保证肿瘤区域得到准确的剂量和减少正常组织受量,PTV外扩边界理论上应不小于0.4 cm.

Research on the safety target margin in intensity-modulated radiation therapy of nasopharyngeal carcinoma

Objective:To investigate setup error during intensity modulated radiation therapy (IMRT) for nasopharyngeal carcinoma and provide the basis for margin of planning target volune(PTV) by EPID(electronic portal imaging device),and to insure the radiation treatment planning more scientific and reasonable.Methods:Fifty NPC patients were enrolled in this study,whose electronic portal images were acquired by " blind" mode before treatment and weekly.The data can be used to calculate the margin from CTV to PTV according to the formula MPTV =2.5 ∑ + 2.5σ.Results:The average setup error of NPC patients' were (0.004 6 ± 0.087 5) cm in left-right direction,(0.048 3 ±0.065 1) cm in superior-inferior direction and (0.027 2 ±0.137 3) cm in anterior-posterior direction.The target margin were 0.1 cm in left-right direction,0.4 cm in superior-inferior and anterior-posterior direction.Conclusion:The data of patients setup error by the way of image guided can be used for estimating the safety target margin.In order to ensure the patients'target totally irradiated and protect the more normal tissue to avoid unnecessary irradiation,the PTV expanding boundary should not be less than 0.4 cm in theory.