前列腺癌图像引导放疗中锥形束CT为合成CT提供质量保证的可行性研究

Feasibility study of cone-beam CT for quality assurance of synthetic CT in image-guided radiotherapy for prostate cancer

目的:探究在基于MR的前列腺癌(prostate cancer,PCa)图像引导放疗(image guided radiotherapy,IGRT)中锥形束CT(cone beam CT,CBCT)为合成CT(synthetic CT,sCT)提供质量保证(quality assurance,QA)的可行性。方法:以CT作为QA的金标准,进行体外实验和临床试验。体外实验:利用仿真人体模型检验CBCT的CT值的长期稳定性并建立CBCT的CT值-电子密度曲线。临床试验:筛选2021年6月至2022年12月间于某院接受诊疗且符合纳入标准的PCa患者10例,所有患者均于IGRT前3 d进行1.5T MR和CT扫描。基于患者的MR图像生成sCT图像后进行放疗计划设计和治疗。将患者的sCT、CT和CBCT图像进行基于黄金基准标志物(gold fiducial marker,GFM)的融合配准后,拷贝sCT放疗计划至CT和CBCT图像上并计算剂量分布,分别比较sCT和CT、sCT和CBCT的Gamma通过率和剂量体积直方图(dose volume histogram,DVH)指标。采用SPSS 19.0软件进行统计学分析。结果:体外实验表明,CBCT的CT值(CT值CBCT)长期稳定性良好,与CT的CT值(CT值CT)的一元回归方程为CT值CBCT=1.110×CT值CT+3.891。临床试验表明,sCT和CT、sCT和CBCT在横断面、冠状面、矢状面上的Gamma通过率均呈高度正相关,具有高度一致性,差异平均值均小于0.1%;DVH各项指标差异均较为接近,且均呈高度正相关。结论:在基于MR的PCa IGRT中,CBCT可取代金标准CT为sCT提供QA。

Objective To explore the feasibility of cone beam CT(CBCT)to provide quality assurance(QA)for synthetic CT(sCT)in MR-based image guided radiotherapy(IGRT)for prostate cancer(PCa).Methods In vitro experiments and clinical trials were carried out using CT as the gold standard for quality assurance.The long-term stability of the CT value of CBCT was examined using a simulated human model and the CT value-electron density curve of CBCT was established in in vitro experiment.During clinical trials 10 PCa patients treated in some hospital from June 2021 to December 2022 were selected according to the inclusion criteria,and underwent 1.5T MR and CT scans 3 d before IGRT.Radiotherapy plan design and treatment were performed after generating sCT images based on the patients'MR images.After the sCT,CT and CBCT images of the patients were fused and aligned based on the gold fiducial marker(GFM),the sCT radiotherapy plans were copied to the CT and CBCT images and the dose distributions were calculated,and the Gamma pass rates and the indexes of dose volume histogram(DVH)were compared between sCT and CT and between sCT and CBCT,respectively.SPSS 19.0 software was used for statistical analysis.Results In vitro experiments showed the CT value of CBCT had long-term stability,and the univariate regression equation was HUCBCT=1.110×HUCT+3.891.Clinical trials proved that the Gamma pass rates of sCT and CT,sCT and CBCT in the transverse,coronal,and sagittal planes were highly positively correlated and highly consistent,with the mean differences lower than 0.1%;the differences in each of the DVH indexes were relatively close to each other,and were all highly positively correlated.Conclusion CBCT can replace the gold standard CT to provide QA for sCT in MR-based PCa IGRT.