Department of Radiation Oncology, School of Medicine, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Med Phys. 2010 Sep;37(9):5092-101. doi: 10.1118/1.3480962.
To experimentally validate a new algorithm for reconstructing the 3D positions of implanted brachytherapy seeds from postoperatively acquired 2D conebeam-CT (CBCT) projection images.
The iterative forward projection matching (IFPM) algorithm finds the 3D seed geometry that minimizes the sum of the squared intensity differences between computed projections of an initial estimate of the seed configuration and radiographic projections of the implant. In-house machined phantoms, containing arrays of 12 and 72 seeds, respectively, are used to validate this method. Also, four 103Pd postimplant patients are scanned using an ACUITY digital simulator. Three to ten x-ray images are selected from the CBCT projection set and processed to create binary seed-only images. To quantify IFPM accuracy, the reconstructed seed positions are forward projected and overlaid on the measured seed images to find the nearest-neighbor distance between measured and computed seed positions for each image pair. Also, the estimated 3D seed coordinates are compared to known seed positions in the phantom and clinically obtained VariSeed planning coordinates for the patient data.
For the phantom study, seed localization error is (0.58 +/- 0.33) mm. For all four patient cases, the mean registration error is better than 1 mm while compared against the measured seed projections. IFPM converges in 20-28 iterations, with a computation time of about 1.9-2.8 min/ iteration on a 1 GHz processor.
The IFPM algorithm avoids the need to match corresponding seeds in each projection as required by standard back-projection methods. The authors' results demonstrate approximately 1 mm accuracy in reconstructing the 3D positions of brachytherapy seeds from the measured 2D projections. This algorithm also successfully localizes overlapping clustered and highly migrated seeds in the implant.
从术后获得的二维锥形束 CT（CBCT）投影图像中，实验验证一种重建植入近距离放射治疗种子三维位置的新算法。
迭代正向投影匹配（IFPM）算法寻找三维种子几何形状，该形状最小化初始种子配置计算投影与植入物放射投影之间的平方强度差之和。使用内部加工的包含分别包含 12 个和 72 个种子的体模来验证该方法。另外，对 4 个 103Pd 植入后的患者使用 ACUITY 数字模拟器进行扫描。从 CBCT 投影集中选择 3 到 10 个 X 射线图像，并对其进行处理以创建仅包含种子的二进制图像。为了量化 IFPM 的准确性，将重建的种子位置正向投影并与测量的种子图像叠加，以找到每个图像对中测量种子位置和计算种子位置之间的最近邻距离。另外，还将估计的三维种子坐标与体模中的已知种子位置以及患者数据的临床获得的 VariSeed 计划坐标进行比较。
对于体模研究，种子定位误差为（0.58 +/- 0.33）mm。对于所有四个患者病例，与测量的种子投影相比，平均配准误差优于 1mm。IFPM 在 20-28 次迭代中收敛，在 1GHz 处理器上的计算时间约为 1.9-2.8 分钟/次。
IFPM 算法避免了标准反向投影方法所需的在每个投影中匹配相应种子的需求。作者的结果表明，从测量的二维投影中重建近距离放射治疗种子的三维位置的精度约为 1mm。该算法还成功定位了植入物中重叠的密集和高度迁移的种子。
