食管癌患者CBCT图像剂量计算准确性的分析评估

Accuracy of dose calculation with CBCT images in patients with esophageal cancer

目的:分析探讨食管癌患者利用锥形束CT(CBCT)图像进行剂量计算应用的可行性。方法:选择8例经过旋转调强放疗的食管癌患者,利用自主研发ART软件实现患者扇形束CT(kVCT)和首分次CBCT的准确形变配准及计划映射,同时采用直方图匹配方法对CBCT的HU值进行修正;将所得CBCT计划导入到原系统采用kVCT的HU-ED曲线及跳数重新完成剂量计算。结果:CBCT图像中各组织接受剂量及体积参数相对于kVCT偏差绝对值均小于1%。按照2 mm/2%/TH:10%标准,CBCT图像中各组织接受剂量相对于kVCT平均γ通过率均达99%以上。按照1 mm/1%/TH:10%标准,靶区平均γ通过率下降明显,最低为(82.59±16.16)%;各危及器官平均γ通过率仍可达98%以上。结论:本研究结果充分验证CBCT图像剂量计算精度,为自适应放疗中采用CBCT图像直接进行剂量计算奠定一定基础。

Objective To analyze the feasibility of using cone beam (CBCT) images for dose calculation in patients with esophageal cancer. Methods Eight patients receiving rotational intensity-modulated radiotherapy for esophageal cancer were enrolled in this study. Self-developed ART software was used to achieve accurate deformation registration and plan mapping of kVCT and the first fractional CBCT, and meanwhile histogram matching method was used to modify the HU values of CBCT. The obtained CBCT plans were imported into the original system. Finally, the HU-ED curve of kVCT was combined with monitor units for dose recalculation. Results The absolute deviations of dose and volume parameters of tissues in CBCT images from those in KCT images were less than 1%. According to the standard of 2 mm/2%/TH: 10%, the average gamma passing rate of each tissue received in the CBCT image relative to kVCT was over 99%. According to the standard of 1 mm/1%/TH: 10%, the mean gamma passing rates of target areas decreased significantly, with the lowest being 82.59%±16.16%, and the gamma passing rates of organsat-risk were still above 98%. Conclusion The results fully verified the accuracy of dose calculation with CBCT image, and laid a certain foundation for direct dose calculation with CBCT images in adaptive radiotherapy.