Purpose

The objective of this work is to estimate the patient positioning accuracy of a surface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS).

Methods

Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as a basis for determination of positioning accuracy. A total of 35 patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a “standard” and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile.

Results

The interfractional measurement displacement vector of the SGRT system, σ_SGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σ_SGRT increased by about 20%. The standard deviation of the axis-related σ_SGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σ_SGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σ_SGRT, MC simulations served as a measure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5 mm cannot be ruled out. In contrast, MC simulations resulted in a positioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly a change in the facial surface relative to a defined point in the brain.

Conclusion

In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.

中文翻译：

---

光学表面引导和 X 射线引导成像的患者摆位精度对颅内立体定向放射治疗影响的比较

目的

这项工作的目的是评估使用光学表面扫描仪的表面引导放射治疗 (SGRT) 系统与基于 X 射线的成像系统 (IGRT) 的患者定位精度，以及它们对颅内立体定向放射治疗的影响（SRT）和颅内立体定向放射外科（SRS）。

方法

患者定位数据均通过同一直线加速器上的 SGRT 和 IGRT 系统采集，作为确定定位精度的基础。使用 X 射线立体成像对总共 35 名戴着两种不同开放式面罩（578 个数据集）的患者进行定位，并使用 SGRT 记录开放式面罩内的患者位置。使用 IGRT 和 SGRT 患者定位数据集评估 SGRT 系统（在“标准”和更高分辨率的 SRS 模式下）的测量精度，同时考虑到 X 射线系统的测量误差。根据这些临床测量数据集，使用蒙特卡罗 (MC) 模拟估计定位精度。作为颅脑 SRT 实践标准的相关评估标准是第 95 个百分位数。

结果

SGRT 系统的分数间测量位移矢量σ _SGRT在高分辨率模式下估计为 2.5 毫米（第 68 个百分位）和 5 毫米（第 95 个百分位）。如果使用标准分辨率，σ _SGRT增加约 20%。SGRT 系统的轴相关σ _SGRT的标准偏差在分数间范围为 1.5 至 1.8 mm，在分数内范围为 0.5 至 1.0 mm。σ _SGRT的大小主要取决于患者表面扫描的原理，而不是由于软件或硬件的技术限制或供应商特定问题。基于所得的σ _SGRT，MC 模拟可作为非共面沙发旋转定位精度的衡量标准。如果 SGRT 系统用作非共面区域中唯一的患者定位设备，则不能排除高达 6 毫米的分次间定位误差和高达 5 毫米的分次内定位误差。相比之下，使用 IGRT 系统进行 MC 模拟时，定位误差为 1.6 毫米（第 95 个百分点）。SGRT 系统中定位误差的原因主要是面部表面相对于大脑中定义点的变化。

结论

为了在颅脑立体定向放射治疗中实现必要的几何精度，强烈建议使用基于 X 射线的 IGRT 系统，特别是在使用非共面治疗床角度进行治疗时。