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.

中文翻译：

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关于在螺旋断层扫描设备上实施自适应放射治疗的兆伏计算机断层扫描设置的建议。

在Accuray Radixact装置上评估了兆伏计算机断层扫描（MVCT）图像质量指标，以推荐扫描设置以实施一致的自适应放射治疗程序。评估了兆伏计算机断层扫描图像质量，并使用商用锥束计算机断层扫描图像质量体模将其与千伏CT（kVCT）模拟器进行了比较。在Accuray Radixact上使用细，正常和粗节距获取兆伏计的计算机断层扫描，并使用所有可用的重建切片厚度，每个切片厚度均使用标准和迭代重建（IR）进行重建。使用DoseLab评估图像质量指标（IQM）：自动和手动计算的空间分辨率，对象对比度和对比度-噪声比（CNR）。精细扫描时间为15.6 s / cm，正常扫描时间为8.1 s / cm，粗间距为5.6 s / cm。对于标准重建，自动评估的空间分辨率的范围分别为0.39、0.41至0.42 lp / mm，对于软组织IR，其自动分辨率的范围分别为0.24、0.21至0.18 lp / mm。kVCT的空间分辨率测得至少为0.42 lp / mm。在MVCT设置中，对比度保持一致，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，普通IR的7.4±0.4，软组织IR的12.0±1.9。已经发现，对于给定的间距，增加重建片的厚度并不能改善IQM。基于不同音高值之间对比度指标的一致性，以及使用法线与小音高相比仅略微降低的空间分辨率，我们建议使用2 mm切片厚度的标准间距，以最大程度地提高ART的图像质量，同时限制扫描时间。仅对于需要改进CNR并且可接受的降低空间分辨率的站点，才建议使用软组织IR。