IBM Almaden Research Center, San Jose, CA, 95120, USA.
Philips Research North America, Cambridge, MA, 02141, USA.
Med Phys. 2018 Jun;45(6):2357-2368. doi: 10.1002/mp.12894. Epub 2018 Apr 24.
Intraoperative dosimetry in low-dose-rate (LDR) permanent prostate brachytherapy requires accurate localization of the implanted seeds with respect to the prostate anatomy. Transrectal Ultrasound (TRUS) imaging, which is the main imaging modality used during the procedure, is not sufficiently robust for accurate seed localization. We present a method for integration of electromagnetic (EM) tracking into LDR prostate brachytherapy procedure by fusing it with TRUS imaging for seed localization.
Experiments were conducted on five tissue mimicking phantoms in a controlled environment. The seeds were implanted into each phantom using an EM-tracked needle, which allowed recording of seed drop locations. After each needle, we reconstructed a 3D ultrasound (US) volume by compounding a series of 2D US images acquired during retraction of an EM-tracked TRUS probe. Then, a difference image was generated by nonrigid registration and subtraction of two consecutive US volumes. A US-only seed detection method was used to detect seed candidates in the difference volume, based on the signature of the seeds. Finally, the EM-based positions of the seeds were used to detect the false positives of the US-based seed detection method and also to estimate the positions of the missing seeds. After the conclusion of the seed implant process, we acquired a CT image. The ground truth for seed locations was obtained by localizing the seeds in the CT image and registering them to the US coordinate system.
Compared to the ground truth, the US-only detection algorithm achieved a localization error mean of 1.7 mm with a detection rate of 85%. By contrast, the EM-only seed localization method achieved a localization error mean of 3.7 mm with a detection rate of 100%. By fusing EM-tracking information with US imaging, we achieved a localization error mean of 1.8 mm while maintaining a 100% detection rate without any false positives.
Fusion of EM-tracking and US imaging for prostate brachytherapy can combine high localization accuracy of US-based seed detection with the robustness and high detection rate of EM-based seed localization. Our phantom experiments serve as a proof of concept to demonstrate the potential value of integrating EM-tracking into LDR prostate brachytherapy.
低剂量率（LDR）永久性前列腺近距离放射治疗中的术中剂量学需要精确确定植入的种子相对于前列腺解剖结构的位置。在手术过程中主要使用的直肠超声（TRUS）成像对于精确的种子定位来说不够稳健。我们提出了一种将电磁（EM）跟踪集成到 LDR 前列腺近距离放射治疗程序中的方法，通过将其与 TRUS 成像融合来进行种子定位。
在受控环境下对五个组织模拟体模进行了实验。使用 EM 跟踪针将种子植入每个体模中，这允许记录种子的掉落位置。在每次进针后，我们通过组合 EM 跟踪 TRUS 探头缩回过程中获取的一系列 2D US 图像来重建 3D US 体积。然后，通过非刚性配准和减去两个连续的 US 体积来生成差异图像。基于种子的特征，我们使用仅基于 US 的种子检测方法在差异体积中检测种子候选物。最后，使用 EM 确定的种子位置来检测 US 检测方法的假阳性，并估计缺失种子的位置。在种子植入过程结束后，我们获取了 CT 图像。种子位置的地面实况是通过在 CT 图像中定位种子并将其注册到 US 坐标系来获得的。
与地面实况相比，仅基于 US 的检测算法的定位误差平均值为 1.7mm，检测率为 85%。相比之下，仅基于 EM 的种子定位方法的定位误差平均值为 3.7mm，检测率为 100%。通过将 EM 跟踪信息与 US 成像融合，我们在保持 100%检测率且无任何假阳性的情况下，实现了 1.8mm 的定位误差平均值。
将 EM 跟踪与 US 成像融合用于前列腺近距离放射治疗可以将基于 US 的种子检测的高精度与基于 EM 的种子定位的稳健性和高检测率相结合。我们的体模实验证明了将 EM 跟踪集成到 LDR 前列腺近距离放射治疗中的概念验证的潜在价值。
