3种图像模式在影像引导放射治疗中的差异性研究

目的 检测并分析电子射野影像系统( EPID)、kV级平面摄像(kV planar)、kV级锥形束CT( CBCT)3种图像模式在影像引导放疗(IGRT)中摆位误差的精度.方法 通过在计划系统的模体CT图像上模拟25组摆位偏差,生成25组DRR参考图像和25组三维CT参考图像,分别与模体在原点位置获取的EPID,kV planar和CBCT 3种图像模式进行图像配准和摆位误差的测量,检测并比较3种图像模式在摆位误差测量中的精度.结果 共读取675组残留误差,3种图像及其相应的配准方法均具有较高的精确度,残留误差的平均值在x、y、z方向上均＜1 mm,CBCT的灰度值配准精度＜0.1 mm,kV planar图像在手动配准时其测量摆位误差的精度好于EPID(＜0.65 mm),在自动配准方法时与EPID具有同等的精度.结论 医院IGRT系统的3种图像模式及其相应的配准方法均可以满足临床应用,CBCT为首选,结合图像质量、成像剂量和配准精度等因素,kV planar优于EPID.

A comparision of three imaging modalities in image-guided radiotherapy

Objective To investigate and analyze the positioning accuracy of three imaging modalities utilized in image-guided radiotherapy (IGRT): electronic portal imaging device (EPID), kV portal image (kV planar) and the kV cone beam computed tomography (CBCT).Methods 25 groups of setup errors were simulated on the phantom images through treatment planning system. Digitally reconstructed radiographs (DRRs) were constructed from the CT data which were subsequently used as references to register the EPID and kV planar images acquired at the original position. In addition, the reconstructed 3D-CT images were used to register the CBCT images. Finally, the setup errors using several registration methods were measured to investigate and compare the accuracies of the three imaging modalities used for patient setup. Results 675 groups of residual errors were analyzed. All combinations of imaging modalities and registration method were found to be accurate. The mean residual errors in three directions were less than 1 mm. The method based on grey value match of CBCT images was found as the most accurate with an uncertainty below 0.1 mm. When the manual match was used, the performance of kV planar was more accurate than that of EPID (residual error <0.65 mm). If automatic registration was applied, kV planar generated similar results as EPID did. Conclusions The three available imaging modalities and their corresponding registration methods are all competent for the clinical application of IGRT in our department. Considering the image quality, radiation dose and the accuracy of registration, CBCT has the priority on IGRT followed by the kV planar.