新型立式CT系统用于直立位放射治疗模拟与治疗计划的技术评估
Technical assessment of a novel vertical CT system for upright radiotherapy simulation and treatment planning
AI总结：
本研究评估了一种新型立式CT系统，其图像质量和剂量计算精度满足光子和质子放射治疗要求，成像剂量适中，空间完整性良好。
摘要：
目的：表征一种配备六自由度患者定位系统的立式CT扫描仪的图像质量、成像剂量和剂量计算精度。方法：在120 kVp和200 mAs条件下测量成像剂量（CTDIvol）。使用ACR-464模体评估图像质量。在已知材料插入物内评估平均CT值准确性，并通过均匀模体中心与周边值的差异评估均匀性。通过可见线对和调制传递函数（MTF）评估高对比度分辨率。通过对比噪声比（CNR）量化低对比度性能。在相距100 mm的基准标记之间评估空间完整性。进行了亨斯菲尔德单位到质量密度和阻止本领比的校准。在异质和均质区域的胸部模体立式CT扫描上优化质子和光子治疗计划。在配准的卧式CT扫描上正向计算剂量，并使用3D伽马分析评估一致性。结果：16 cm头部模体的CT成像剂量（CTDIvol）为23.5 mGy，32 cm体部模体为10.1 mGy。水的平均CT值（HU）为1.7，丙烯酸为120.8，均在预期范围内。空气（-950.4）、聚乙烯（-78.8）和骨（823.0）的CT值略微超出范围（5-27 HU）。20 cm和48 cm直径模体的图像均匀性分别为20.2 HU和35.0 HU。可观察到8个高对比度线对。MTF在50%处为4.4 cm-1，在10%处为7.1 cm-1。中位CNR为0.93，低于1.0的容差。空间完整性为0.36 mm。在1%/1mm标准下，光子和质子计划的伽马通过率分别为99.8%和90.6%，在3%/2mm标准下所有计划的通过率均大于或等于98.0%。结论：立式CT的图像质量和剂量计算精度可满足光子和质子放射治疗的要求。
英文摘要：
Purpose: To characterize image quality, imaging dose, and dose calculation accuracy for an upright CT scanner with a six-degree-of-freedom patient positioning system. Methods: Imaging dose (CTDIvol) was measured at 120 kVp and 200 mAs. Image quality was evaluated using an ACR-464 phantom. Mean CT number accuracy was assessed within inserts of known material and uniformity as the difference in values at the center and periphery of uniform phantoms. High-contrast resolution was assessed by visible line pairs and modulation transfer function (MTF). Low-contrast performance was quantified by contrast-to-noise-ratio (CNR). Spatial integrity was evaluated between fiducials 100 mm apart. Hounsfield unit to mass density and stopping-power-ratio calibrations were performed. Proton and photon treatment plans were optimized on upright CT scans of a thorax phantom in heterogenous and homogeneous regions. Dose was forward computed on a registered recumbent CT scan and agreement evaluated using 3D gamma analysis. Results: CT imaging dose (CTDIvol) was 23.5 mGy for the 16 cm head phantom and 10.1 mGy for the 32 cm body phantom. Mean CT numbers (HU) were within the expected range for water (1.7) and acrylic (120.8). CT numbers were slightly (5-27 HU) out-of-range for air (-950.4), polyethylene (-78.8), and bone (823.0). Image uniformity was 20.2 HU and 35.0 HU for 20 cm and 48 cm diameter phantoms, respectively. Eight high-contrast line pairs were visualized. The MTF equaled 4.4 cm-1 at 50% and 7.1 cm-1 at 10%. The median CNR was 0.93, below the 1.0 tolerance. Spatial integrity was 0.36 mm. Gamma pass rates were 99.8% for photon and 90.6% for proton plans with 1%/1mm criteria, and greater than or equal to 98.0% for all plans with 3%/2mm criteria. Conclusion: Upright CT image quality and dose calculation accuracy are acceptable for photon and proton radiotherapy.
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