图像配准条件对头颈部CBCT引导放疗精度影响

Impacts of registration parameters on accuracy of cone-beam computed tomography image-guided head and neck radiotherapy

目的：明确头颈部CBCT引导放疗图像层厚与配准范围对自动配准精度的影响，为IGRT摆位修正提供参考依据。方法以1、3 mm层厚获取头颈部仿真模体的计划CT图像，并在加速器上模拟x、y、z方向摆位偏差，进行CBCT扫描和1、3 mm层厚重建图像。分别设置不同配准框范围（范围1：眼眶上缘至第七颈椎中间；范围2：颅顶至第七颈椎中间）对上述两种层厚CBCT与计划CT图像进行自动配准，评估配准精度。结果配准范围1在1、3 mm层厚图像配准误差为x方向（0．5±0．2）、（－0．7±0．2） mm （P＝0．00），y方向（0．5±0．3）、（1．0±0．3） mm （P＝0．00），z方向（－0．1±0．5）、（1．5±0．5） mm （P＝0．00）。配准范围2在3 mm层厚图像配准误差为x方向（－0．4±0．2） mm，y方向（0．5±0．2） mm，z方向（0．7±0．4） mm。结论在头颈部CBCT或CT图像配准中将颅顶包含进配准范围内能显著提高配准的精度。采用1 mm层厚图像配准的误差可以控制在1 mm内。

Objective To evaluate the impacts of slice thickness and registration frame range on the accuracy of cone-beam computed tomography （ CBCT） image-guided head and neck （ HN） radiotherapy, and to provide a basis for positioning correction in image-guided radiotherapy.Methods A planned CT scan was performed for an anthropomorphic HN phantom with slice thickness of 1 mm and 3 mm and simulated positioning errors in x, y, and z directions on the accelerator.CBCT scan and reconstruction were performed with slice thickness of 1 mm and 3 mm.Two different registration frame ranges were used （ range 1：from C7 to superior orbit;range 2：from C7 to calvaria ） .Automatic bony registration was performed for CBCT and planned CT images with slice thickness of 1 mm and 3 mm.The registration accuracy was evaluated.Results For range 1, the registration errors in x, y, and z directions with a slice thickness of 1 mm were significantly lower than those with a slice thickness of 3 mm （0.5±0.2 mm vs.-0.7±0.2 mm, P=0.00;0.5±0.3 mm vs. 1.0±0.3 mm, P=0.00;-0.1±0.5 mm vs.1.5±0.5 mm, P=0.00）.For range 2, the registration errors in x, y, and z directions with a slice thickness of 3 mm were-0.4±0.2 mm, 0.5±0.2 mm, and 0.7±0.4 mm, respectively.Conclusions Engagement of calvaria in registration range can substantially enhance the registration accuracy in CBCT or CT images for HN.The registration error with slice thickness of 1 mm can be controlled within 1 mm.