Departments of Radiation Oncology, Stanford University, Stanford, CA, 94305, USA.
Departments of Mechanical Engineering, Stanford University, Stanford, CA, 94305, USA.
Med Phys. 2017 May;44(5):1857-1864. doi: 10.1002/mp.12207. Epub 2017 Apr 17.
A correct body contour is essential for reliable treatment planning in radiation therapy. While modern medical imaging technologies provide highly accurate patient modeling, there are times when a patient's anatomy cannot be fully captured or there is a lack of easy access to computed tomography (CT) simulation. Here, we provide a practical solution to the surface contour truncation problem by using a handheld stereo depth camera (HSDC) to obtain the missing surface anatomy and a surface-surface image registration to stich the surface data into the CT dataset for treatment planning.
For a subject with truncated simulation CT images, a HSDC is used to capture the surface information of the truncated anatomy. A mesh surface model is created using a software tool provided by the camera manufacturer. A surface-to-surface registration technique is used to merge the mesh model with the CT and fill in the missing surface information thereby obtaining a complete surface model of the subject. To evaluate the accuracy of the proposed approach, experiments were performed with the following steps. First, we selected three previously treated patients and fabricated a phantom mimicking each patient using the corresponding CT images and a 3D printer. Second, we removed part of the CT images of each patient to create hypothetical cases with image truncations. Next, a HSDC was used to image the 3D-printed phantoms and the HSDC-derived surface models were registered with the hypothetically truncated CT images. The contours obtained using the approach were then compared with the ground truth contours derived from the original simulation CT without image truncation. The distance between the two contours was calculated in order to evaluate the accuracy of the method. Finally, the dosimetric impact of the approach is assessed by comparing the volume within the 95% isodose line and global maximum dose (D ) computed based on the two surface contours for the breast case that exhibited the largest contour variation in the treated breast.
A systematic strategy of using a 3D HSDC to compensate for missing surface information caused by the truncation of CT images was established. Our study showed that the proposed technique was able to reliably provide the full contours for treatment planning in the case of severe CT image truncation(s). The root-mean-square error for the registration between the aligned HDSC surface model and the ground truth data was found to be 2.1 mm. The average distance between the two models was 0.4 ± 1.7 mm (mean ± SD). Maximum deviations occurred in areas of high concavity or when the skin was close to the couch. The breast tissue covered by 95% isodose line decreased by 3% and D increased by 0.2% with the use of the HSDC model.
The use of HSDC for obtaining missing surface data during simulation has a number of advantages, such as, ease of use, low cost, and no additional ionizing radiation. It may provide a clinically practical solution to deal with the longstanding problem of CT image truncations in radiation therapy treatment planning.
在放射治疗中，正确的身体轮廓对于可靠的治疗计划至关重要。虽然现代医学成像技术为患者建模提供了高度的准确性，但有时患者的解剖结构无法完全捕获，或者难以进行计算机断层扫描（CT）模拟。在这里，我们通过使用手持立体深度相机（HSDC）获取缺失的表面解剖结构，并使用表面到表面图像配准将表面数据拼接至 CT 数据集以进行治疗计划，提供了一种解决表面轮廓截断问题的实用方法。
对于模拟 CT 图像截断的患者，使用 HSDC 捕获截断解剖结构的表面信息。使用相机制造商提供的软件工具创建网格表面模型。使用表面到表面的配准技术将网格模型与 CT 融合，并填充缺失的表面信息，从而获得患者的完整表面模型。为了评估所提出方法的准确性，我们进行了以下实验步骤。首先，我们选择了三名已接受治疗的患者，并使用相应的 CT 图像和 3D 打印机制作了模拟每个患者的模型。其次，我们从每个患者的 CT 图像中去除部分图像，以创建具有图像截断的假设病例。接下来，使用 HSDC 对 3D 打印的模型进行成像，并将 HSDC 生成的表面模型与假设的截断 CT 图像进行配准。然后，将使用该方法获得的轮廓与未进行图像截断的原始模拟 CT 获得的真实轮廓进行比较。计算两个轮廓之间的距离以评估方法的准确性。最后，通过比较基于两个表面轮廓计算的接受治疗乳房的 95%等剂量线内体积和全局最大剂量（D），评估该方法的剂量学影响。
我们建立了一种使用 3D HSDC 补偿 CT 图像截断引起的表面信息缺失的系统策略。研究表明，该技术能够在严重的 CT 图像截断情况下可靠地提供治疗计划的完整轮廓。配准后 HDSC 表面模型与真实数据之间的均方根误差为 2.1mm。两个模型之间的平均距离为 0.4±1.7mm（均值±标准差）。最大偏差发生在高度凹陷区域或皮肤靠近治疗床的部位。使用 HSDC 模型后，95%等剂量线覆盖的乳房组织减少了 3%，D 增加了 0.2%。
在模拟过程中使用 HSDC 获取缺失的表面数据具有易用性、低成本和无额外电离辐射等优点。它可能为处理放射治疗计划中 CT 图像截断这一长期存在的问题提供一种临床实用的解决方案。
