Cheek Dennis, Gee Victoria, Bernard Mark E, Molloy Janelle
Department of Radiation Medicine, Markey Cancer Center, University of Kentucky, Lexington, KY.
Department of Radiation Medicine, Markey Cancer Center, University of Kentucky, Lexington, KY.
Brachytherapy. 2019 Sep-Oct;18(5):683-688. doi: 10.1016/j.brachy.2019.05.010. Epub 2019 Jun 24.
The CivaSheet device uses multiple directionally shielded Pd-103 CivaDot sources to produce a directional planar dose distribution. In postplanning, manually digitizing the 3D source orientation is challenging because the 3D vector must be digitized by using 2D displayed images. The aim of this study is to develop an algorithm that will automatically determine the direction of each CivaDot source based on the location of sources adjacent to it.
The algorithm determines the source direction by averaging the normal directions of multiple local planes established by the adjacent sources. The algorithm was tested on a manually constructed CivaSheet-like device that was CT scanned in known flat geometries and two known curved geometries. Algorithmically determined source directions were compared with the known directions. The algorithm was also used on a postplan for a gynecological pelvic sidewall tumor bed implant and compared against manual digitization of the source directions.
For the flat and curved test geometries, the average angular difference between the algorithm determined and known orientation was 1.2° ± 0.8° (flat geometry), 1.7° ± 2.1° (curve about vertical axis), and 2.3° ± 2.4° (curve about horizontal axis). For the patient case, results showed on average a 23.1° ± 10.8° difference between the manual digitized orientation and the algorithm's predicted orientation.
The algorithm calculates the source orientation with accuracy better than 2.3° for the controlled experiments. In addition to its accuracy, the algorithm produces consistent results and lessens the difficult challenge of orienting the partially shielded sources.
CivaSheet 设备使用多个定向屏蔽的 Pd - 103 CivaDot 源来产生定向平面剂量分布。在计划后期，手动数字化三维源方向具有挑战性，因为必须通过二维显示图像来数字化三维向量。本研究的目的是开发一种算法，该算法将基于相邻源的位置自动确定每个 CivaDot 源的方向。
该算法通过对由相邻源建立的多个局部平面的法向方向求平均来确定源方向。该算法在一个手动构建的类似 CivaSheet 的设备上进行测试，该设备在已知的平面几何形状和两种已知的弯曲几何形状下进行了 CT 扫描。将算法确定的源方向与已知方向进行比较。该算法还用于妇科盆腔侧壁肿瘤床植入的计划后期，并与源方向的手动数字化进行比较。
对于平面和弯曲测试几何形状，算法确定的方向与已知方向之间的平均角度差为 1.2°±0.8°（平面几何形状）、1.7°±2.1°（绕垂直轴弯曲）和 2.3°±2.4°（绕水平轴弯曲）。对于患者病例，结果显示手动数字化方向与算法预测方向之间平均相差 23.1°±10.8°。
对于对照实验，该算法计算源方向的精度优于 2.3°。除了其准确性外，该算法产生一致的结果，并减轻了确定部分屏蔽源方向的困难挑战。
