目的: 通过由图像引导的加速器配备的锥形束CT( Cone beam CT，CBCT) 了解本中心现有的定位方
式引起的临床上的摆位误差，指导制定放射治疗计划过程中的PTV( planning target volume) 外放范围。方法: 在
放射治疗过程中，完成病人摆位后拍摄病人的锥形束CT 图像与治疗计划设计时的CT 图像的匹配，获得病人的
摆位误差，把其平均值和标准差分别做为系统误差和随机误差，通过公式MPTV( 外放) = 2． 5Σ+0． 7σ 获得三维方
向上的肿瘤靶区外放边界。结果: 得到校位前病人三个方向的外放数据如下X = 5． 80mm，Y = 6． 22mm，Z
= 5． 06mm。校位后病人三个方向上的外放数据如下: X = 2． 55mm，Y = 2． 79mm，Z = 1． 93mm。结论: 图像引导放
射治疗方式可有效减小肿瘤靶区的外放边界，两种治疗方式应选择不同的外放边界。

Objective: To study the positioning errros data caused by positioning method， the data
were obtained from CBCT images and were used to guide the PTV margin clinically． Methods: CBCT
images during the course of radiotherapy after completion of patient positioning were matched with CT
images of the treatment planning， then the mean value and standard deviation of the positioning errros
data were obtained， the external tumor target boundaries In three dimensions direction were obtained by
the formula of MPTV( free) = 2． 5Σ +0． 7σ and systematic errors and random errors as the mean value
and standard deviation of the positioning errros data． Results: The external data in three directions precorrection
as follows: X= 5． 80mm，Y= 6． 22mm，Z = 5． 06mm， the external data in three directions post
－correction as follows: X = 2． 55mm，Y = 2． 79mm，Z = 1． 93mm． Conclusion: Image － guided radio －
therapy methods can effectively reduce the external tumor target boundaries，both treatment methods
should choose a different external boundaries．

R815

 收稿日期: 2013－07－06; 修回日期: 2013－09－15
基金项目: 内蒙古自然科学基金( 2010MS1145)
作者简介: 乌晓礼( 1972－) ，男，内蒙古医科大学附属医院放疗科物理师，理学硕士。
通讯作者: 郁志龙，教授E－mail: richard_yu1961269@ sina． com． 内蒙古医科大学放射科， 010050