基于Livermore模型CT图片构建人体躯干数字体模及其在肺部计数器虚拟刻度中的应用

VOXEL PHANTOM BASED ON THE CT IMAGES OF LIVERMORE TORSO PHANTOM AND ITS APPLICATION IN VIRTUAL CALIBRATION OF A REAL IN-VIVO LUNG COUNTING SYSTEM

基于Livermore人体躯干物理模型CT图片构建数字体模,并结合蒙特卡罗程序MCNP对一套由四个宽能高纯锗探测器(BEGe)构成的肺部计数器进行了虚拟刻度。首先,利用点源(241Am,137Cs,^(60)Co,54Mn,57Co,109Cd)实验数据,对高纯锗晶体尺寸进行调整以获得正确的探测器几何参数,在γ射线能量13.9keV～1332.5keV范围内,调整后四个探测器全能峰效率实验测量的平均值与蒙特卡罗计算值的差别在±10%范围内。之后,对不同胸壁厚度(CWT=19mm,25mm,30mm,43mm)躯干体模进行CT扫描获得其CT图片,利用Dosigray软件对CT图片进行分割后,连同探测器几何描述文件输入到OEDIPE软件,生成数字体模虚拟刻度用MCNP输入程序。最后,利用241Am、152Eu肺部源对数字体模虚拟刻度结果进行了实验验证,结果表明:在59.5keV～1408keV能量范围内,虚拟刻度结果与实验结果的差别在±10%之间;对于17.5keV能量,差别在±30%之间。

Voxel phantom is created based on the CT images of Livermore torso phantom, the application of voxel phantom in virtual calibration of a real in-vivo lung counting system, composed of an array of four Broad Energy high purity Germanium detectors （BEGe）, is performed using Monte Carlo method. At the first step, geometry parameters of the detector are properly specified by comparisons of FEPE （Full Energy Peak Efficiency） between Monte Carlo calculations and the average measured values of four BEGe detectors using point sources （^241 Am, ^137 Cs,^60 Co,^54 Mn,^57 Co, ^109 Cd）. The differences of FEPE between calculations and measurements are generally within ± 10% for gamma rays in the energy range of 13.9 keV to 1332.5 keV. Then, the CT images of Livermore phantom with different overlay plates （ CWT = 19 mm, 25 mm, 30 mm, 43 mm） are segmented by Dosigray software, and inputted into OEDIPE together with the detectors＇ geometry description to create the MCNP input-file for virtual calibration purpose. Finally, the validation of virtual calibration with voxel phantom is done using lung sources （^241 Am,^152 Eu）, The comparisons between virtual calibration and physical phantom experiments show that relative deviations are within ± 10% in the energy range of 59.5 keV - 1408 keV, and within ± 30% for 17.5 keV photons.