In linear accelerator-based stereotactic irradiation (STI) for brain metastasis, cone-beam computed tomography (CBCT) image quality is essential for ensuring precise patient setup and tumor localization. However, CBCT images may be degraded by the deviation of the CBCT isocenter from the brain center. This study aims to investigate the effects of the distance from the brain center to the CBCT isocenter (DBI) on the image quality in STI. An anthropomorphic phantom was scanned with varying DBI in right, anterior, superior, and inferior directions. Thirty patients undergoing STI were prospectively recruited. Objective metrics, utilizing regions of interest included contrast-to-noise ratio (CNR) at the centrum semiovale, lateral ventricle, and basal ganglia levels, gray and white matter noise at the basal ganglia level, artifact index (AI), and nonuniformity (NU). Two radiation oncologists assessed subjective metrics. In this phantom study, objective measures indicated a degradation in image quality for non-zero DBI. In this patient study, there were significant correlations between the CNR at the centrum semiovale and lateral ventricle levels (r_s = − 0.79 and − 0.77, respectively), gray matter noise (r_s = 0.52), AI (r_s = 0.72), and NU (r_s = 0.91) and DBI. However, no significant correlations were observed between the CNR at the basal ganglia level, white matter noise, and subjective metrics and DBI (r_s < ± 0.3). Our results demonstrate the effects of DBI on contrast, noise, artifacts in the posterior fossa, and uniformity of CBCT images in STI. Aligning the CBCT isocenter with the brain center can aid in improving image quality.

在基于直线加速器的脑转移立体定向照射 (STI) 中，锥形束计算机断层扫描 (CBCT) 图像质量对于确保精确的患者摆位和肿瘤定位至关重要。然而，CBCT 图像可能会因 CBCT 等角点偏离大脑中心而降低质量。本研究旨在探讨脑中心到CBCT等中心点（DBI）的距离对STI图像质量的影响。使用不同的 DBI 在右、前、上、下方向扫描拟人模型。前瞻性招募了 30 名患有性传播感染的患者。客观指标，利用感兴趣区域包括半卵圆中心、侧脑室和基底神经节水平的对比度噪声比（CNR）、基底神经节水平的灰质和白质噪声、伪影指数（AI）和不均匀性（努）。两名放射肿瘤学家评估了主观指标。在这项模型研究中，客观测量表明非零 DBI 的图像质量下降。在这项患者研究中，半卵圆中心和侧脑室水平的 CNR（分别为 r _s = − 0.79 和 − 0.77）、灰质噪声（r _s = 0.52）、AI（r _s = 0.72）之间存在显着相关性。 、NU (r _s = 0.91) 和 DBI。然而，基底神经节水平的 CNR、白质噪声以及主观指标和 DBI 之间没有观察到显着相关性 (r _s < ± 0.3)。我们的结果证明了 DBI 对 STI 中 CBCT 图像的对比度、噪声、后颅窝伪影和均匀性的影响。将 CBCT 等角点与大脑中心对齐有助于提高图像质量。