Department of Radiation Oncology, Dana-Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, Massachusetts 02115, USA.
Med Phys. 2010 Aug;37(8):4414-23. doi: 10.1118/1.3464716.
To balance dose reduction and image registration accuracy in breast setup imaging. In particular, the authors demonstrate the relationship between scan angle and dose delivery for cone beam tomosynthesis (CBTS) when employed for setup verification of breast cancer patients with surgical clips.
The dose measurements were performed in a female torso phantom for varying scan angles of CBTS. Setup accuracy was measured using three registration methods: Clip centroid localization accuracy and the accuracy of two semiautomatic registration algorithms. The dose to the organs outside of the ipsilateral breast and registration accuracy information were compared to determine the optimal scan angle for CBTS for breast patient setup verification. Isocenter positions at the center of the patient and at the breast-chest wall interface were considered.
Image registration accuracy was within 1 mm for the CBTS scan angles theta above 20 degrees for some scenarios and as large as 80 degrees for the worst case, depending on the imaged breast and registration algorithm. Registration accuracy was highest based on clip centroid localization. For left and right breast imaging with the isocenter at the chest wall, the dose to the contralateral side of the patient was very low (<0.5 cGy) for all scan angles considered. For central isocenter location, the optimal scan angles were 30 degrees - 50 degrees for the left breast imaging and 40 degrees - 50 degrees for the right breast imaging, with the difference due to the geometric asymmetry of the current clinical imaging system.
The optimal scan angles for CBTS imaging were found to be between 10 degrees and 50 degrees, depending on the isocenter location and ipsilateral breast. Use of the isocenter at the breast-chest wall locations always resulted in greater accuracy of image registration (<1 mm) at smaller angles (10 degrees - 20 degrees) and at lower doses (<0.1 cGy) to the contralateral organs. For chest wall isocenters, doses delivered to organs outside of the target breast were much smaller than the scattered and leakage doses of the treatment beams. The complete volumetric information of all clips in the region of interest, combined with the small dose to the contralateral organs and the small scan angle, could result in an advantage for small angle CBTS with off center isocenters over simple orthogonal pairs.
在乳房设置成像中平衡剂量减少和图像配准精度。特别是，作者展示了当使用手术夹进行乳腺癌患者设置验证时，锥形束断层摄影术（CBTS）的扫描角度与剂量传递之间的关系。
在女性躯干模型中进行了不同 CBTS 扫描角度的剂量测量。使用三种注册方法测量了设置精度：夹芯定位精度和两种半自动注册算法的精度。将器官外的剂量与注册准确性信息进行比较，以确定用于乳腺癌患者设置验证的 CBTS 的最佳扫描角度。考虑了患者中心和乳房胸壁界面的等中心位置。
对于某些情况，CBTS 扫描角度 theta 大于 20 度，某些情况下最大为 80 度，图像注册准确性在 1 毫米以内，具体取决于成像乳房和注册算法。基于夹芯芯定位的注册准确性最高。对于左、右乳房成像，当等中心位于胸壁时，所有考虑的扫描角度对患者对侧的剂量都非常低（<0.5 cGy）。对于中央等中心位置，左乳房成像的最佳扫描角度为 30 度至 50 度，右乳房成像的最佳扫描角度为 40 度至 50 度，差异源于当前临床成像系统的几何不对称性。
根据等中心位置和同侧乳房，CBTS 成像的最佳扫描角度在 10 度至 50 度之间。在较小角度（10 度至 20 度）和较低剂量（<0.1 cGy）下，将等中心置于乳房胸壁位置始终可以实现更高的图像配准精度（<1 毫米），而对非靶器官的剂量则较小。对于胸壁等中心，靶区外器官的剂量比治疗束的散射和泄漏剂量小得多。感兴趣区域内所有夹的完整容积信息，结合对非靶器官的小剂量和小扫描角度，可能会使偏心等中心的小角度 CBTS 相对于简单的正交对具有优势。
