基于Varian锥形束CT影像质量的直线加速器选择策略

目的:定量分析不同锥形束CT（CBCT）影像特点，从而为患者选择最佳设备。方法:利用CatPhan604模体分析Edge、TrueBeam及新旧ix机载CBCT头、胸、盆模式图像。结果:12组图像头、胸、盆CT值最准确的是ix新机器、TrueBeam、Edge，分别为5.69、0.81、6.74 HU；CT值线性最好的是ix旧机器或新机器、Edge、Edge，分别为0.995、0.996、0.997；线性距离误差最小的是ix旧机器、Edge、Edge或TrueBeam或ix旧机器，分别为0.050、0.075、0.100 mm；角度误差最小的是ix旧机器、Edge或TrueBeam、Edge或ix新机器，分别为0.075°、0.050°、0.075°。头、胸、盆高对比度分辨率最好的是ix旧机器、Edge、Edge，分别为7、5、5 LP/cm；均匀性最好的是Edge、Edge、Edge，分别为4.78、20.19、4.63。头、胸、盆噪声最好的是Edge、ix新机器、ix新机器，分别为27.53、8.67、7.33；信噪比最好的是Edge、TrueBeam、ix新机器，分别为83.17、124.39、288.39；对比度噪声比最好的是Edge、ix新机器、ix新机器，分别为11.92、41.42、51.47。低对比度分辨率头部未可见，胸、盆部最好的是Edge或TrueBeam、Edge，分别为6.00、3.75。结论:CBCT系统间差异大，为患者选择加速器时应考虑成像特点，如自适应放疗选择高CT值线性和准确性，立体定向放疗选择低距离和角度误差设备等。

LINAC selection strategy based on quality of Varian cone beam CT image

Abstract: Objective To quantitatively analyze the features of different cone beam CT (CBCT) images for selecting the optimal LINAC for patients. Methods CatPhan604 phantom was used for evaluating the quality of the images of head, thorax and pelvis which were obtained by 4 CBCT mounted on an Edge, a TrueBeam, and 2 ix (ix New and ix Old). Results Of the 12 image sets, the best accurate CT number for the head, thorax and pelvis was observed on ix New, TrueBeam, and Edge, respectively, and the corresponding value was 5.69, 0.81, 6.74 HU, respectively. The best CT number linearity was found on ix New or ix Old (0.995), Edge (0.996), and Edge (0.997), respectively. Moreover, ix Old, Edge, and Edge or TrueBeam or ix Old had the minimal linear distance errors, which were 0.050, 0.075, 0.100 mm, respectively; and ix Old, Edge or TrueBeam, and Edge or ix New had the smallest angular errors, which were 0.075°, 0.050°, and 0.075°, respectively. For the head, thorax and pelvis, the best contrast resolution (7, 5, and 5 LP/cm, respectively) was achieved by ix Old, Edge, and Edge, respectively; and the best homogeneity (4.78, 20.19, and 4.63, respectively) was obtained by Edge, Edge, and Edge. The lowest noise for the head, thorax and pelvis was observed on Edge, ix New, and ix New, which were 27.53, 8.67, and 7.33, respectively; the best signal-to-noise ratio was observed on Edge, TrueBeam, and ix New, which were 83.17, 124.39, and 288.39, respectively; and the best contrast-to-noise ratio was observed on Edge, ix New, and ix New, which were 11.92, 41.42, and 51.47, respectively. No low contrast resolution was found in the head, while Edge or TrueBeam, and Edge achieved the best low contrast resolution (6.00 and 3.75) for thorax and pelvis. Conclusion Large inter-system varieties are observed among different CBCT systems. When choosing an appropriate machine for a special patient, imaging features should also be considered. For instance, LINAC with CBCT that can provide better CT number linearity and accuracy should be assigned for a patient undergoing adaptive radiotherapy, while machines with lower distance and angular errors should be chosen for patients having stereotactic radiotherapy.