Velten Christian, Boyd Robert, Jeong Kyoungkeun, Garg Madhur K, Tomé Wolfgang A
Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY, USA.
Albert Einstein College of Medicine, Bronx, NY, USA.
J Appl Clin Med Phys. 2020 May;21(5):87-92. doi: 10.1002/acm2.12859. Epub 2020 Mar 26.
Megavoltage computed tomography (MVCT) image quality metrics were evaluated on an Accuray Radixact unit to recommend scan settings for the implementation of a consistent adaptive radiotherapy program. Megavoltage computed tomography image quality was evaluated and compared to a kilovoltage CT (kVCT) simulator using a commercial cone beam computed tomography image quality phantom. Megavoltage computed tomographies were acquired on the Accuray Radixact using fine, normal, and coarse pitches, with all available reconstruction slice thicknesses, each of which were reconstructed using standard and iterative reconstruction (IR). Image quality metrics (IQM) were evaluated using DoseLab: automatically and manually calculated spatial resolution, subject contrast, and contrast-to-noise ratio (CNR). Scanning time was 15.6 s/cm for fine, 8.1 s/cm for normal, and 5.6 s/cm for coarse pitch. Automatically evaluated spatial resolutions ranged from 0.39, 0.41, to 0.42 lp/mm for standard reconstruction and from 0.24, 0.21, to 0.18 lp/mm for soft-tissue IR, respectively, with general IR yielding values in between these. Spatial resolution for kVCT was measured to be at least 0.42 lp/mm. Contrast was consistent across MVCT settings with 8.1 ± 0.2%, while kVCT contrast was 10.27 ± 0.05%. CNR was calculated to be 3.3 ± 0.4 for standard reconstruction, 7.4 ± 0.4 for general IR, and 12.0 ± 1.9 for soft-tissue IR. It was found that increasing reconstruction slice thickness for a given pitch does not improve IQMs. Based on the consistency of contrast metrics across pitch values and the only slightly reduced spatial resolution using normal compared to fine pitch, we recommend the use of normal pitch with 2 mm slice thickness to maximize image quality for ART while limiting scanning time. Only for sites for which improved CNR is required and reduced spatial resolution is acceptable, soft-tissue IR is recommended.
在一台Accuray Radixact设备上评估了兆伏级计算机断层扫描（MVCT）图像质量指标，以推荐扫描设置，用于实施一致的自适应放射治疗计划。使用商用锥束计算机断层扫描图像质量体模评估兆伏级计算机断层扫描图像质量，并与千伏级CT（kVCT）模拟器进行比较。在Accuray Radixact上使用精细、正常和粗糙螺距采集兆伏级计算机断层扫描图像，采用所有可用的重建切片厚度，每种厚度均使用标准重建和迭代重建（IR）进行重建。使用DoseLab评估图像质量指标（IQM）：自动和手动计算空间分辨率、主体对比度和对比度噪声比（CNR）。精细螺距的扫描时间为15.6秒/厘米，正常螺距为8.1秒/厘米，粗糙螺距为5.6秒/厘米。标准重建的自动评估空间分辨率分别为0.39、0.41至0.42线对/毫米，软组织IR为0.24、0.21至0.18线对/毫米，一般IR产生的值介于两者之间。kVCT的空间分辨率测量为至少0.42线对/毫米。MVCT设置下的对比度一致，为8.1±0.2%，而kVCT对比度为10.27±0.05%。标准重建的CNR计算为3.3±0.4，一般IR为7.4±0.4，软组织IR为12.0±1.9。研究发现，对于给定螺距增加重建切片厚度并不会改善IQM。基于螺距值之间对比度指标的一致性以及与精细螺距相比，正常螺距仅略微降低空间分辨率，我们建议使用2毫米切片厚度的正常螺距，以在限制扫描时间的同时最大化ART的图像质量。仅对于需要提高CNR且可接受降低空间分辨率的部位，建议使用软组织IR。
