应用KV-CBCT校正直肠癌IMRT摆位误差的研究

Study on correction of IMRT setup error of rectal cancer by KV-CBCT

目的使用千伏级锥形束CT(KV-CBCT)实时在线校正直肠癌调强适形放疗(IMRT)的摆位误差,确定直肠癌患者放疗计划外扩边界的范围,分析体质量差别对摆位的影响。方法 42例接受IMRT的直肠癌患者,按照体质量指数(BMI)分为A组(BMI≥24 kg/m2)和B组(BMI<24 kg/m2),各21例。将CBCT与计划CT图像进行灰度自动配准,计算摆位误差并进行在线评价。结果 42例患者在X轴(左右)、Y轴(头脚)、Z轴(前后)方向摆位误差分别为(1.1±2.3)、(2.1±5.0)、(-1.1±2.2)mm,外放边界为5.3、10.9、5.7 mm。A组患者在Y方向摆位误差较B组增大,差异有统计学意义(P<0.05)。两组在X、Z方向摆放误差比较差异无统计学意义(P>0.05)。结论应用KV-CBCT在线校正可减小直肠癌患者摆位误差,并利用摆位误差估算放疗摆位外扩边界值,BMI大者应适当增加外扩边界。

Objective To determine the scope of external boundary expansion for radiotherapy planning and analyze the impact of body mass difference on setup by using kilovoltage cone beam CT（KV-CBCT） for realtime online correction of setup errors of rectal cancer in three dimensional intensity modulated radiation therapy（IMRT）.Methods A total of 42 rectal cancer patients with IMRT were divided by body mass index [BMI,weight/height（kg/m^2）] into group A（BMI ≥ 24 kg/m^2） and group B（BMI24 kg/m^2）,with 21 cases in each group.The CBCT was automatically registered with the planned CT image,and the position error was calculated and evaluated on-line.Results 42 patients had setup error at X axis（left and right）,Y axis（head and foot） and Z axis（front and back） respectively as（1.1±2.3）,（2.1±5.0） and（-1.1±2.2） mm,and the margin were 5.3,10.9,5.7 mm.Group A had larger setup error at Y axis,and the difference had statistical significance（P〈0.05）.Both groups had no statistically significant difference in setup error at X and Z axis（P〈0.05）.Conclusion Application of KVCBCT online correction can reduce the setup errors of rectal cancer patients and estimate the external expansion boundary values of radiotherapy settings by using the position error,and the external expansion boundary of larger BMI should be increased appropriately.