不同图像引导方式在头颈部肿瘤中成像剂量测量

Measurement of the Imaging Dose for Head and Neck Cancer by Different Image-guided Methods

目的测量不同图像引导方式在头模中的成像剂量。方法应用UNIDOS E型剂量仪(德国PTW公司)与30013型电离室,测量Varian Clinac iX直线加速器配置的EPID、OBI和CBCT图像引导功能在圆柱形模体的成像剂量。二维图像采用0o和270o两个正交野成像,三维图像采用CBCT成像。结果二维成像时,OBI系统(KV级X线)模体内各点平均吸收剂量0.74mGy,显著低于EPID系统(MV级X线)的90.93mGy,且图像清晰度优于后者;标准CBCT(KV级X线)各点平均吸收剂量4.77mGy,而低剂量CBCT模式仅为标准模式的50%,能够完成精确匹配。结论OBI系统比EPID系统成像剂量更低,图像质量更好。CBCT作为三维图像引导方式显著优于二维图像引导方式,进行日常的摆位验证也是安全的。因此,合理选择图像引导方式和设置图像采集参数,能够有效地减少患者的额外受照剂量。

Objective To measure the imaging dose in the head phantom by different image-guided methods.Methods The imaging dose was measured in a cylindrical phantom on a Varian Clinac iX linear accelerator equipped with EPID,OBI,CBCT using a PTW 0.6cc ion chamber with UNIDOS E dosimeter.2D images were acquired by two perpendicular fields（0o270o）,and the 3D images by CBCT.Results The 2D imaging average dose for OBI（KV X-ray） was 0.74mGy in the head phantom.It was significantly lower than 90.93mGy for EPID（MV X-ray） and the image quality was better.For a standard CBCT（KV X-ray）,the imaging average dose was 4.77mGy.For a low dose mode,the imaging dose was 50% of the standard mode.Moreover,3D images could match accurately.Conclusion For the OBI system,the imaging dose is lower and image quality is better than EPID.The 3D image-guided method for CBCT is better than 2D and is also safe for daily position verification.Therefore,during treatment positioning,the appropriate image-guide methods and scanning parameters can effectively reduce the additional dose to the patients.