不同模体采集的CT-电子密度转换曲线分析研究

Analysis and study of CT-electron density conversion curves collected from different phantoms

目的:通过比较CATphan504模体和CIRS062模体采集的电子密度转换曲线,分析探讨厂家自带多功能CATphan504模体采集的CT-电子密度转换曲线用于治疗计划系统剂量计算的可行性。方法:在CT模拟定位机相同扫描参数下对两个模体进行CT扫描,利用CT操作控制系统对模体内不同组织电子密度模块进行采集记录,将两个模体实际测量的CT值(HU)录入治疗计划系统,生成两条不同的CT-电子密度转换校准曲线。选取患者的3个不同治疗部位计划进行剂量计算,比较加速器跳数(MU)照射剂量MU值及中心层面剂量分布变化情况。结果:CATphan504模体和CIRS062模体采集的CT-电子密度转化曲线有明显区别,尤其CATphan504模体高密度组织曲线拟合效果较差。不同CT-电子密度转换曲线下胸部、腹部和盆腔计划的MU数值两个模体误差分别为0.9%、1%和1.3%。CATphan504模体盆腔中心层面上剂量曲线分布低剂量区无变化,靶区内高剂量区有较小变化。结论:CATphan504模体内接近人体组织的电子密度模块种类较少,高密度组织中CT值变化大,两模体CT电子密度转换曲线有差异,CATphan504模体不能完全替代CIRS062模体做CT电子密度转换曲线的剂量校准。

Objective:To analyze and explore the feasibility of the computed tomography(CT)-electron density conversion curve,which was collected from multi-functional CATphan504 phantom that came from CT manufacturer,was used in dose calculation of treatment plan system through compared the electron density conversion curves of CATphan504 phantom and CIRS062 phantom.Methods:Computed tomography(CT)scan was performed on the two phantoms under the same scan parameters of CT simulated locator.The electron density modules of different tissues in the phantom were collected and recorded by the CT operation control system.The actual measured CT values(HU)of two phantoms were recorded into the treatment plan system to generate two different CT-electron density conversion calibration curves.The plans of three different treatment sites of patients were selected for conducting dose calculation,and the MU value of exposure dose of accelerator machine unit(MU)and the change of dose distribution at the level of center were compared.Results:There was obviously differences in the collected CT electron density conversion curves between CATphan504 phantom and CIRS062 phantom,and the fitting effect of CATphan504 phantom was especially poor for the tissue of high-density.The errors of MU values of two phantoms on thoracic,abdominal and pelvic plans were 0.9%,1%and 1.3%under different CT-electron density conversion curves,respectively.There was change in low dose region of dose curve distribution on the level of the center of pelvic cavity of CATphan504 phantom,and the change was lesser in high dose region within target region.Conclusion:There are a few types of electron density modules that are close to human tissue in CATphan504 phantom,and the changes of CT values are great in the high-density tissue.There are differences in CT electron density conversion curves between two phantoms,and CATphan504 phantom cannot completely replace the CIRS062 phantom to conduct dose calibration of CT electron density conversion curves.