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.
National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China.
Phys Med. 2017 Apr;36:110-118. doi: 10.1016/j.ejmp.2017.03.023. Epub 2017 Apr 4.
To improve the image quality and accuracy of dose calculation for cone-beam computed tomography (CT) images through implementation of a dual-energy cone-beam computed tomography method (DE-CBCT), and evaluate the improvement quantitatively.
Two sets of CBCT projections were acquired using the X-ray volumetric imaging (XVI) system on a Synergy (Elekta, Stockholm, Sweden) system with 120kV (high) and 70kV (low) X-rays, respectively. Then, the electron density relative to water (relative electron density (RED)) of each voxel was calculated using a projection-based dual-energy decomposition method. As a comparison, single-energy cone-beam computed tomography (SE-CBCT) was used to calculate RED with the Hounsfield unit-RED calibration curve generated by a CIRS phantom scan with identical imaging parameters. The imaging dose was measured with a dosimetry phantom. The image quality was evaluated quantitatively using a Catphan 503 phantom with the evaluation indices of the reproducibility of the RED values, high-contrast resolution (MTF), uniformity, and signal-to-noise ratio (SNR). Dose calculation of two simulated volumetric-modulated arc therapy plans using an Eclipse treatment-planning system (Varian Medical Systems, Palo Alto, CA, USA) was performed on an Alderson Rando Head and Neck (H&N) phantom and a Pelvis phantom. Fan-beam planning CT images for the H&N and Pelvis phantom were set as the reference. A global three-dimensional gamma analysis was used to compare dose distributions with the reference. The average gamma values for targets and OAR were analyzed with paired t-tests between DE-CBCT and SE-CBCT.
In two scans (H&N scan and body scan), the imaging dose of DE-CBCT increased by 1.0% and decreased by 1.3%. It had a better reproducibility of the RED values (mean bias: 0.03 and 0.07) compared with SE-CBCT (mean bias: 0.13 and 0.16). It also improved the image uniformity (57.5% and 30.1%) and SNR (9.7% and 2.3%), but did not affect the MTF. Gamma analyses of the 3D dose distribution with criteria of 1%/1mm showed a pass rate of 99.0-100% and 85.3-97.6% for DE-CBCT and 73.5-99.1% and 80.4-92.7% for SE-CBCT. The average gamma values were reduced significantly by DE-CBCT (p< 0.05). Gamma index maps showed that matching of the dose distribution between CBCT-based and reference was improved by DE-CBCT.
DE-CBCT can achieve both better image quality and higher accuracy of dose calculation, and could be applied to adaptive radiotherapy.
通过实施双能锥束计算机断层扫描方法（DE-CBCT）来提高锥束计算机断层扫描（CT）图像的质量和剂量计算的准确性，并对这种改进进行定量评估。
使用X射线容积成像（XVI）系统在Synergy（医科达，斯德哥尔摩，瑞典）系统上分别以120kV（高）和70kV（低）X射线获取两组CBCT投影。然后，使用基于投影的双能分解方法计算每个体素相对于水的电子密度（相对电子密度（RED））。作为比较，使用单能锥束计算机断层扫描（SE-CBCT）通过由具有相同成像参数的CIRS体模扫描生成的亨氏单位-RED校准曲线来计算RED。使用剂量测定体模测量成像剂量。使用Catphan 503体模通过RED值的可重复性、高对比度分辨率（MTF）、均匀性和信噪比（SNR）等评估指标对图像质量进行定量评估。在Alderson Rando头颈部（H&N）体模和骨盆体模上使用Eclipse治疗计划系统（瓦里安医疗系统公司，帕洛阿尔托，加利福尼亚州，美国）对两个模拟容积调强弧形治疗计划进行剂量计算。将H&N和骨盆体模的扇形束计划CT图像设置为参考。使用全局三维伽马分析将剂量分布与参考进行比较。通过DE-CBCT和SE-CBCT之间的配对t检验分析靶区和危及器官的平均伽马值。
在两次扫描（H&N扫描和体部扫描）中，DE-CBCT的成像剂量分别增加了1.0%和减少了1.3%。与SE-CBCT（平均偏差：0.13和0.16）相比，它具有更好的RED值可重复性（平均偏差：0.03和0.07）。它还改善了图像均匀性（分别为57.5%和30.1%）和SNR（分别为9.7%和2.3%），但不影响MTF。以1%/1mm为标准的3D剂量分布伽马分析显示，DE-CBCT的通过率为99.0 - 100%和85.3 - 97.6%，SE-CBCT的通过率为73.5 - 99.1%和80.4 - 92.7%。DE-CBCT使平均伽马值显著降低（p < 0.05）。伽马指数图显示，DE-CBCT改善了基于CBCT的剂量分布与参考之间的匹配。
DE-CBCT可以实现更好的图像质量和更高的剂量计算准确性，并可应用于自适应放疗。
