Patient positing accuracy.

The purpose of this study was to determine the residual patient positioning error of ocular proton treatment based on daily setup X-ray images and tantalum clips. The residual day-to-day patient positioning accuracy in a cohort of 60 patients and 240 fractions was determined in two steps. The 3D tantalum clips’ positions in the orthogonal X-ray images just prior to aperture placement were registered with 3D clips’ positions derived from the reference data from treatment planning. The aperture, placed before irradiation, reduced the field of view in axial images blocking clips partially or completely in most cases. The clips’ positions after aperture placement in the lateral images were compared with the reference clips’ positions. Partially visible clips in the axial image were registered to the clips in the axial image prior to aperture placement. The day-to-day deviations to aperture placement were corrected with the registration results for translations only. The residual day-to-day patient position variations just prior to irradiation were −0.06 ± 0.27 mm (mean ± 1SD) for the left-right direction, −0.01 ± 0.23 mm for the anterior-posterior direction and −0.01 ± 0.19 mm for the superior-inferior direction. This data was further investigated by differentiating for treated eye, gazing eye and the use of eyelid retractor. This yielded no significant differences. The residual patient positioning errors are small for patients treated at the dedicated eyeline, indicating that the patient positioning workflow using tantalum clips is highly accurate. The reported errors can be used for ocular proton margin calculations and for the evaluation of a clipless ocular proton therapy workflow.本研究旨在基于每日摆位X射线影像与钽夹（tantalum clips），明确眼部质子治疗中的患者摆位残余误差。本研究通过两步法，对60例患者共240个治疗分次的队列中，患者每日摆位的残余精度进行了测定。在照射前放置限光筒（aperture）前获取的正交X线影像中，钽夹的三维位置，与治疗计划参考数据导出的钽夹三维位置完成配准。多数情况下，照射前放置的限光筒会缩小轴向影像的视野，对钽夹造成部分或完全遮挡。将侧位影像中限光筒放置后的钽夹位置，与参考钽夹位置进行比对；对于轴向影像中部分可见的钽夹，则将其与限光筒放置前的轴向影像中的钽夹完成配准。仅通过配准结果，对限光筒放置前的每日摆位偏差进行平移校正。照射即刻的每日患者摆位残余变异情况为：左右方向-0.06±0.27 mm（均值±1倍标准差），前后方向-0.01±0.23 mm，上下方向-0.01±0.19 mm。本研究进一步根据受累眼、注视眼及眼睑拉钩（eyelid retractor）的使用情况进行分组分析，未发现各组间存在显著差异。在专用眼部治疗通道接受治疗的患者，其摆位残余误差极小，表明采用钽夹的患者摆位流程具备极高的精准度。本研究报告的误差数据可用于眼部质子治疗的靶区边缘计算，以及无钽夹眼部质子治疗流程的评估。