Gregg Kenneth W, Arsenault Theodore, Rezaei Atefeh, Kashani Rojano, Henke Lauren, Price Alex T
Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Cleveland, Ohio, USA.
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA.
J Appl Clin Med Phys. 2025 Aug;26(8):e70145. doi: 10.1002/acm2.70145.
Current cone-beam computed tomography (CBCT) on-board c-arm linear accelerators (linacs) lack CT number precision sufficient for dose calculation due to increased scatter from the cone geometry. This investigation evaluated CT number and dose calculation accuracy in-phantom on a novel on-board CBCT unit with potential for improved dose calculation accuracy.
Eight head and eight body configurations of an electron density phantom using 16 materials were acquired with a clinical CT-simulator(CT-sim) and novel on-board CBCT imager. CBCT projection data was reconstructed using conventional Feldkamp-Davis-Kress(FDK) and patient scatter-corrected iterative Acuros CTS with metal artifact reduction (Acuros-CTS-iCBCT-MAR) to create a robust CT number to physical density curve. CT-sim and CBCT images of anthropomorphic head and thorax phantoms were acquired, and three treatment plans were generated per phantom. All CBCT images were registered to the CT-sim of the phantoms, and the dose was recalculated on the CBCT images. 3D gamma analysis was performed (10% dose threshold, local, 1% dose difference, 1 or 2 mm distance to agreement), and dose-volume histogram (DVH) metrics were reported for target coverage and organ sparing.
CT numbers for materials ≤1.08 g/cc showed high agreement between CT-sim and CBCT acquisitions. CT number precision improved with Acuros-CTS-iCBCT-MAR compared to FDK in all materials. High agreement between CT-sim and CBCT reconstructed with Acuros-CTS-iCBCT-MAR was observed in 3D gamma analysis showing 93.8% voxels passing in the worst case for a spine stereotactic body radiotherapy (SBRT) plan at 1%/1 mm. Maximum deviation in target coverage was -3.3% PTV-D98% in the lung SBRT plan among the novel reconstructed CBCT images. Plan comparison using FDK reconstructions yielded similar or worse agreement in 3D gamma analysis, with 69.7% voxels passing in the worst case for a spine SBRT treatment plan. Maximum target coverage deviation was -11.7% PTV-D98% among the FDK-reconstructed CBCT.
Novel CBCT solutions on c-arm linacs show promise for enabling direct-to-unit or offline adaptive dose calculation, potentially increasing versatility and efficiency of patient-centered care.
由于锥形几何结构导致散射增加，当前锥形束计算机断层扫描（CBCT）机载C型臂直线加速器（直线加速器）缺乏足以进行剂量计算的CT值精度。本研究评估了一种新型机载CBCT设备在体模内的CT值和剂量计算准确性，该设备具有提高剂量计算准确性的潜力。
使用16种材料的电子密度体模的8种头部和8种身体配置，通过临床CT模拟机（CT-sim）和新型机载CBCT成像仪进行采集。使用传统的菲尔德坎普-戴维斯-克雷斯（FDK）算法和患者散射校正迭代Acuros CTS并减少金属伪影（Acuros-CTS-iCBCT-MAR）重建CBCT投影数据，以创建一条稳健的CT值与物理密度曲线。采集拟人化头部和胸部体模的CT-sim和CBCT图像，每个体模生成三个治疗计划。所有CBCT图像都与体模的CT-sim进行配准，并在CBCT图像上重新计算剂量。进行三维伽马分析（10%剂量阈值，局部，1%剂量差异，1或2毫米距离一致性），并报告剂量体积直方图（DVH）指标以评估靶区覆盖和器官保护情况。
密度≤1.08 g/cc的材料的CT值在CT-sim和CBCT采集之间显示出高度一致性。与FDK相比，Acuros-CTS-iCBCT-MAR在所有材料中均提高了CT值精度。在三维伽马分析中观察到，使用Acuros-CTS-iCBCT-MAR重建的CT-sim和CBCT之间具有高度一致性，在脊柱立体定向体部放射治疗（SBRT）计划的最坏情况下，1%/1毫米时93.8%的体素通过。在新型重建的CBCT图像中，肺部SBRT计划中靶区覆盖的最大偏差为PTV-D98%的-3.3%。使用FDK重建进行计划比较在三维伽马分析中产生了相似或更差的一致性，在脊柱SBRT治疗计划的最坏情况下，69.7%的体素通过。在FDK重建的CBCT中，最大靶区覆盖偏差为PTV-D98%的-11.7%。
C型臂直线加速器上的新型CBCT解决方案有望实现直接在设备上或离线进行自适应剂量计算，可能会提高以患者为中心的护理的通用性和效率。
