3DCT扫描模式与运动肿瘤靶体积相关性研究

The correlation between different CT scanning mode and the target volume of movement tumor

目的 研究3DCT在不同扫描速度下获取的运动肿瘤靶区体积及中心位置变化,并确定接近ITV的扫描速度.方法 利用QUASAR呼吸运动模体进行研究,模体内有3 cm×3 cm×3 cm立方体模拟肿瘤运动.以4DCT获得的靶体积为金标准.设置模拟肿瘤运动振幅为0.5、1.0、2.0cm,每一振幅设20、15、10次/min呼吸频率,在每种条件下行不同速度3DCT扫描,扫描12 cm径向长度用时分别为6.6、12.8、31.7 s.计算出3DCT上的靶体积及中心位置,与相应4DCT结果比较.3DCT扫描运动肿瘤靶体积的准确率用靶区长度（30±2） mm的次数/总扫描次数评价.结果 3DCT扫描的准确率为6.8％.扫描时间为6.6、12.8、31.7s时的准确率分别为13％、4％、2％.在振幅为0.5、1.0、2.0 cm下靶区中心位置分别为（318.9±2.75）、（683.2±3.22）、（682.9±4.83） mm;以31.7s扫描时所得靶体积落在ITV-10 mm范围内概率较大,分别占50％、78％、56％.结论 3DCT快速扫描是某一系列随机时相的融合,反映真实肿瘤体积的准确性低.获得的影像中心位置具有随机性,振幅越大或扫描速度越快中心位置变化随机性就越强.

Objective To investigate change of the volume and the epicenter of target volume under different scan speed of the three-dimensional （3D） simulation computed tomography （CT） and determine the scan speed which close to ITV.Methods A dynamic phantom-QUASAR,with a 3 cm × 3 cm × 3 cm target cubic simulating respiratory motion was used.The phantom was set with three different amplitudes and breathing frequencies under different scan speed.The dynamic phantom was also scanned using simulation 4DCT as ITV was the standard.The length of the phantom was 12 cm,the scan time were 6.6 s,12.8 s,31.7 s.The volume and epicenter of the target identified from 3DCT images were calculated and compared to 4DCT images.The number of times of target length （30 ± 2） mm/total scan times was used to assese the accuracy.Results The total accuracy was 6.8％.For different scan speed,the accuracy were 13％,4％ and 2％,respectively.The length of the epicenter of the target volume was （318.9 ±0.37） mm,（683.2 ±0.44） mm,（682.9 ± 0.66） mm under the 0.5 cm,1.0 cm and 2.0 cm,respectively.When the scan time was 31.7 s,the volume of the target from the 3DCT were close to ITV-10 mm,the frequency were 50％,78％,56％ for three different amplitude.Conclusions This study shows that the images from the 3D simulation CT were the partial image of the breathing cycle,and the epicenters were diversed with the breathing amplitude and scan speed.The accuracy rate of the 3DCT reflects the real target is low.In addition,the epicenter of the target changed randomly.