技术说明：基于体模的锥形束 CT 剂量计算准确性评估，用于自适应放疗。

Technical note: Phantom-based evaluation of CBCT dose calculation accuracy for use in adaptive radiotherapy.

机构信息

Varian Medical Systems Imaging Laboratory, Daettwil, Switzerland.

Varian Medical Systems, Palo Alto, California, USA.

出版信息

Med Phys. 2024 Oct;51(10):7492-7499. doi: 10.1002/mp.17325. Epub 2024 Aug 5.

DOI:10.1002/mp.17325

PMID:39101716

Abstract

BACKGROUND

High-quality 3D-anatomy of the day is needed for treatment plan adaptation in radiotherapy. For online x-ray-based CBCT workflows, one approach is to create a synthetic CT or to utilize a fan-beam CT with corresponding registrations. The former potentially introduces uncertainties in the dose calculation if deformable image registration is used. The latter can introduce burden and complexity to the process, the facility, and the patient.

PURPOSE

Using the CBCT of the day, acquired on the treatment device, for direct dose calculation and plan adaptation can overcome these limitations. This study aims to assess the accuracy of the calculated dose on the CBCT scans acquired on a Halcyon linear accelerator equipped with HyperSight.

METHODS

HyperSight's new CBCT reconstruction algorithm includes improvements in scatter correction, HU calibration of the imager, and beam shape adaptation. Furthermore, HyperSight introduced a new x-ray detector. To show the effect of the implemented improvements, gamma comparisons of 2%/2 mm, 2%/1 mm, and 1%/1 mm were made between the dose distribution in phantoms calculated on the CBCT reconstructions and the simulation CT scans, considering this the standard of care. The resulting gamma passing rates were compared to those obtained with the Halcyon 3.0 reconstruction and hardware without HyperSight's technologies. Various anatomical phantoms for dosimetric evaluations on brain, head and neck, lung, breast, and prostate cases have been used in this study.

RESULTS

The overall results demonstrated that HyperSight outperformed the Halcyon 3.0 version. Based on the gamma analysis, the calculated dose using HyperSight was closer to the CT scan-based doses than the calculated dose using iCBCT Halcyon 3.0 for most cases. Over all plans and gamma criteria, Halcyon 3.0 achieved an average passing rate of 92.9%, whereas HyperSight achieved 98.1%.

CONCLUSION

Using HyperSight CBCT images for direct dose calculation, for example, in (online) plan adaptation, seems feasible for the investigated cases.

摘要

背景

放射治疗中需要高质量的三维解剖结构来进行治疗计划的调整。对于在线基于 X 射线的 CBCT 工作流程，一种方法是创建合成 CT，或利用具有相应配准的扇束 CT。如果使用变形图像配准，前者可能会导致剂量计算出现不确定性。后者可能会给流程、设备和患者带来负担和复杂性。

目的

使用在治疗设备上获取的当天的 CBCT 进行直接剂量计算和计划调整可以克服这些限制。本研究旨在评估在配备 HyperSight 的 Halcyon 直线加速器上获取的 CBCT 扫描计算得出的剂量的准确性。

方法

HyperSight 的新 CBCT 重建算法包括散射校正、成像仪 HU 校准和射束形状自适应的改进。此外，HyperSight 还引入了新的 X 射线探测器。为了展示所实施改进的效果，在考虑这是标准护理的情况下，对在 CBCT 重建中计算的体模中的剂量分布与模拟 CT 扫描之间的 2%/2mm、2%/1mm 和 1%/1mm 的伽马比较进行了评估。将得到的伽马通过率与 Halcyon 3.0 重建和没有 HyperSight 技术的硬件获得的结果进行了比较。在这项研究中，使用了各种用于脑、头颈部、肺、乳房和前列腺病例剂量评估的解剖体模。

结果

总体结果表明，HyperSight 优于 Halcyon 3.0 版本。基于伽马分析，对于大多数病例，使用 HyperSight 计算得出的剂量比使用 iCBCT Halcyon 3.0 计算得出的剂量更接近 CT 扫描剂量。在所有计划和伽马标准下，Halcyon 3.0 的平均通过率为 92.9%，而 HyperSight 为 98.1%。