Velten Christian, Goddard Lee, Jeong Kyoungkeun, Garg Madhur K, Tomé Wolfgang A
Department of Radiation Oncology, Montefiore Medical Center, Bronx, New York.
Institute for Onco-Physics, Albert Einstein College of Medicine, Bronx, New York.
Adv Radiat Oncol. 2021 Dec 1;7(2):100862. doi: 10.1016/j.adro.2021.100862. eCollection 2022 Mar-Apr.
To assess clinically relevant image quality metrics (IQMs) of helical fan beam kilovoltage (kV) fan beam computed tomography (CT).
kVCT IQMs were evaluated on an Accuray Radixact unit equipped with helical fan beam kVCT to assess the capabilities of this newly available modality. kVCT IQMs were evaluated and compared to a kVCT simulator and linear accelerator-based cone beam CTs (CBCT) using a commercial CBCT image quality phantom. kVCTs were acquired on the Accuray Radixact for all combinations of kVp and mAs in fine mode using a 440-mm field of view (FOV). Evaluated IQMs were spatial resolution, overall uniformity, subject contrast, contrast-to-noise ratio (CNR), and effective slice thickness. Imaging dose was assessed for planar kV imaging.
On this kVCT system spatial resolution and contrast were consistent across all settings with 0.28 ± 0.03 lp/mm and 9.8% ± 0.7% (both 95% confidence interval). CNR strongly depended on selected mode (views per rotation) and body size (mA per view) and ranged between 7.9 and 34.9. Overall uniformity was greater than 97% for all settings. Large FOV was not found to substantially affect the IQMs whereas small FOV affected IQMs due to its effect on pitch. Technique-matched CT simulator scans were comparable for uniformity and contrast, while spatial resolution was higher (0.43 ± 0.06 lp/mm), and CNR was between 4% (140 kVp) and 51% (100 kVp) lower. For kV-CBCT, spatial resolutions ranging from 0.37 to 0.44 lp/mm were achieved with comparable contrast, CNR, and uniformity to kVCT. All kVCT scans exhibit imaging artifacts due to helical acquisition. Clinical acquisitions of megavoltage (MV) CT, kV-CBCT, and kVCT on the same patient showed improved and comparable image quality of kVCT compared to MVCT and kV-CBCT, respectively.
Helical fan beam kVCT allows for daily image guidance for localization and setup verification with comparable performance to existing kV-CBCT systems. Scan parameters must be selected carefully to maximize image quality for the desired tasks. Due to the large effective slice thicknesses for all parameter combinations, kVCT scans should not be used for simulation or planning of stereotactic procedures. Finally, improved image quality over MVCT has the potential to greatly improve manual and automated adaptive monitoring and planning.
评估螺旋扇束千伏（kV）扇束计算机断层扫描（CT）的临床相关图像质量指标（IQM）。
在配备螺旋扇束kVCT的Accuray Radixact设备上评估kVCT IQM，以评估这种新可用模式的性能。使用商业CBCT图像质量体模评估kVCT IQM，并与kVCT模拟器和基于直线加速器的锥束CT（CBCT）进行比较。在Accuray Radixact上使用440毫米视野（FOV），以精细模式采集所有kVp和mAs组合的kVCT。评估的IQM包括空间分辨率、整体均匀性、主体对比度、对比噪声比（CNR）和有效层厚。评估平面kV成像的成像剂量。
在该kVCT系统上，所有设置下的空间分辨率和对比度一致，分别为0.28±0.03 lp/mm和9.8%±0.7%（均为95%置信区间）。CNR强烈依赖于所选模式（每旋转视图数）和身体尺寸（每视图mA），范围在7.9至34.9之间。所有设置下的整体均匀性均大于97%。大FOV未发现对IQM有实质性影响，而小FOV由于其对螺距的影响而影响IQM。技术匹配的CT模拟器扫描在均匀性和对比度方面具有可比性，而空间分辨率更高（0.43±0.06 lp/mm），CNR低4%（140 kVp）至51%（100 kVp）。对于kV-CBCT，实现了0.37至0.44 lp/mm的空间分辨率，其对比度、CNR和均匀性与kVCT相当。所有kVCT扫描由于螺旋采集而表现出成像伪影。对同一患者进行的兆伏（MV）CT、kV-CBCT和kVCT的临床采集显示，与MVCT和kV-CBCT相比，kVCT的图像质量分别有所改善且具有可比性。
螺旋扇束kVCT可为定位和设置验证提供每日图像引导，其性能与现有的kV-CBCT系统相当。必须仔细选择扫描参数，以针对所需任务最大化图像质量。由于所有参数组合的有效层厚较大，kVCT扫描不应用于立体定向程序的模拟或规划。最后，与MVCT相比，图像质量的改善有可能极大地改善手动和自动自适应监测及规划。
