双能锥形束CT线性混合技术提高相对电子密度的准确性  

Relative electron density measurement accuracy improved with linear mix technique on dual energy cone-beam CT

作　　者：门阔[1] 戴建荣[1] 陈辛元[1] 李明辉[1] 张可[1] 黄鹏[1] MEN Kuo DAI Jianrong CHEN Xinyuan LI Minghui ZHANG Ke HUANG Peng(National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021 China)

机构地区：[1]国家癌症中心/中国医学科学院北京协和医学院肿瘤医院,北京100021

出　　处：《中国医学物理学杂志》2017年第5期433-438,共6页Chinese Journal of Medical Physics

基　　金：国家自然科学基金(11605291;11475261);国家重大研发计划(2016YFC0904600)

摘　　要：目的:利用高、低能锥形束CT(CBCT)的线性混合图像校正射线硬化,以提高相对电子密度值(RED)的准确性。方法:使用Elekta公司Synergy加速器的CBCT系统成像,高、低能X线峰值管电压分别为120和70 kV,对比单能CBCT图像采用100 kV。使用铝梯测量高、低能X线穿过不同厚度铝材料的衰减,利用迭代扰动法得到能谱分布,进而确定高、低能图像的最优线性混合系数,得到混合图像HU_(mix),用此图像作为新的CBCT图像,建立HU_(mix)-RED校准曲线,计算物质的RED。使用Catphan 500模体、一个头部仿真模体和一个骨盆部仿真模体进行实验,验证本方法的准确性。结果:头部和骨盆部Catphan 500模体实验得到的RED与理论值的相关系数分别为0.995和0.975,优于单能CBCT(0.975和0.953)。头、骨盆部仿真模体实验也显示,较单能CBCT成像方法,本研究提出的方法能有效减少射线硬化伪影,更准确地测量物质的RED。结论:建立了一种CBCT双能线性混合成像方法,可以较准确地测量物质的RED,为提高自适应放射治疗的精度提供了技术支持。Objective To improve the accuracy of relative electron density （RED） measurement by reducing the beam hardening effect using linear mix technique on dual energy cone-beam CT （CBCT）.Methods CBCT images were obtained using CBCT system of Elekta Synergy linear accelerator with the maximum tube voltage of high-and low-energy X-ray of 120 kV and 70 kV,respectively.As a comparison,single-energy CBCT image was acquired at the tube voltage of 100 kV.When the high-and low-energy X-ray passed through aluminum material of different thickness,the X-ray attenuations were measured using aluminum ladder.And the spectra distribution was obtained with iterative perturbation method to determine the optimal linear mix coefficients of high-and low-energy image,obtaining mixed images Humix.Taking the obtained Humix as the new CBCT images,we established the Humix-RED calibration curve and calculated the RED of the material.Finally,we applied Catphan 500 phantom,head and neck phantom ofAlderson Rando,and pelvis phantom to verify the accuracy of the proposed method.Results The correlation coefficients of the theoretical RED and the RED obtained from Catphan 500 phantom of head and pelvis were 0.995 and 0.975,respectively,better than those obtained from the single-energy CBCT （0.975 and 0.953）.Compared with single-energy CBCT imaging method,the dual-energy CBCT-based method effectively reduced the beam hardening artifacts and measured the RED more accurately.Conclusion The established dual-energy CBCT linear mix imaging method can accurately measure the RED of the material and provide technical support for improving the accuracy of adaptive radiation therapy.

关 键 词：锥形束CT 双能 直线加速器 相对电子密度 自适应放射治疗 

分 类 号：R815.6[医药卫生—放射医学]