虚拟单色CT图像应用于放射治疗计划过程的初步评估

Preliminary evaluation on the application of virtual monochromatic CT image in radiotherapy planning

目的:通过分析宝石光谱成像(GSI)模式下获取的虚拟单色图像的特性,初步评估将其应用于放射治疗计划剂量计算的可行性。方法:采用GE公司的Revolution ES CT扫描系统对CIRS 062M电子密度模体进行扫描;对比不同能量下不同物质的CT测量值与理论值之间的差异;比较间隔26 d的两次扫描CT值;建立单色图像的CT到电子密度(ED)转换曲线。结果:在两次扫描中,不同单色能量下,高密度材料的CT值变化显著,密度小于或等于水的材料的CT值变化较小;较高密度材料(如Dense Bone 800)的CT理论计算值和实测值之间的差异在较低能量时较大;较高能量虚拟单色CT图像的CT-ED转换曲线与普通模式下获得的多色图像一样具有一致的线性关系;但较低能量虚拟单色CT图像的CT-ED转换曲线是双线性。结论:双线性的CT-ED转换曲线可能会带来剂量计算误差,所以将其应用于临床剂量计算时必须选择正确的能量相关CT-ED转换关系。

Objective To analyze the characteristics of virtual monochromatic image obtained using gemstone spectral imaging mode,and to preliminarily evaluate the feasibility of application of virtual monochromatic image in the dose calculation of radiotherapy planning.Methods CIRS 062M electron density phantom was scanned with GE Revolution ES CT scanning system.The differences between measured CT number and theoretical values of different materials at different energies were analyzed.The CT numbers obtained in two scans with an interval of 26 days were compared.Finally,CT to electron density(ED)conversion curves for all monochrome images were established.Results The CT number of highdensity materials changed significantly in the two scans under different monochromatic energies,while the CT number of materials with a density less than or equal to water changed little.For higher-density materials(such as Dense Bone 800),there was obvious difference between theoretical and measured CT numbers at lower energy.The CT-ED conversion curves from higher-energy virtual monochrome CT images had the same linear relationship as the multicolor image obtained in the normal mode;but the CT-ED conversion curves from lower-energy virtual monochrome CT images were bilinear.Conclusion The bilinear CT-ED relationship may lead to errors in dose calculation.Therefore,the correct energy-related CT-ED conversion relationship must be selected when applying virtual monochromatic image to clinical dose calculation.