Department of Biomedical Engineering, Western University, London, ON, N6A 3K7, Canada.
Robarts Research Institute, Western University, London, ON, N6A 5B7, Canada.
Med Phys. 2019 Feb;46(2):800-810. doi: 10.1002/mp.13292. Epub 2018 Dec 7.
Prostate cancer is the most common noncutaneous cancer among men in the USA. Focal laser thermal ablation (FLA) has the potential to control small tumors while preserving urinary and erectile function by leaving the neurovascular bundles and urethral sphincters intact. Accurate needle guidance is critical to the success of FLA. Multiparametric magnetic resonance images (mpMRI) can be used to identify targets, guide needles, and assess treatment outcomes. In this study, we evaluated the location of ablation zones relative to targeted lesions in 23 patients who underwent FLA therapy in a phase II trial. The ablation zone margins and unablated tumor volume were measured to determine whether complete coverage of each tumor was achieved, which would be considered a clinically successful ablation.
Preoperative mpMRI was acquired for each patient 2-3 months preceding the procedure and the prostate and lesion(s) were manually contoured on 3 T T2-weighted axial images. The prostate and ablation zone(s) were also manually contoured on postablation 1.5 T T1-weighted contrast-enhanced axial images acquired immediately after the procedure intraoperatively. The lesion surface was nonrigidly registered to the postablation image using an initial affine registration followed by nonrigid thin-plate spline registration of the prostate surfaces. The margins between the registered lesion and ablation zone were calculated using a uniform spherical distribution of rays, and the volume of intersection was also calculated. Each prostate was contoured five times to determine the segmentation variability and its effect on intersection of the lesion and ablation zone.
Our study showed that the boundaries of the segmented tumor and ablation zone were close. Of the 23 lesions that were analyzed, 11 were completely covered by the ablation zone and 12 were partially covered. A shift of 1.0, 2.0, and 2.6 mm would result in 19, 21, and all tumors completely covered by the ablation zone, respectively. The median unablated tumor volume across all tumors was 0.1 with an IQR of 3.7 , which was 0.2% of the median tumor volume (46.5 with an IQR of 46.3 ). The median extension of the tumors beyond the ablation zone, in cases which were partially ablated, was 0.9 mm (IQR of 1.3 mm), with the furthest tumor extending 2.6 mm.
In all cases, the boundary of the tumor was close to the boundary of the ablation zone, and in some cases, the boundary of the ablation zone did not completely enclose the tumor. Our results suggest that some of the ablations were not clinically successful and that there is a need for more accurate needle tracking and guidance methods. Limitations of the study include errors in the registration and segmentation methods used as well as different voxel sizes and contrast between the registered T2 and T1 MRI sequences and asymmetric swelling of the prostate postprocedurally.
前列腺癌是美国男性中最常见的非皮肤癌。局灶性激光热消融（FLA）有可能在保留神经血管束和尿道括约肌完整的情况下控制小肿瘤，同时保留尿和勃起功能。准确的针引导对 FLA 的成功至关重要。多参数磁共振成像（mpMRI）可用于识别目标、引导针并评估治疗结果。在这项研究中，我们评估了 23 名接受 FLA 治疗的患者的消融区相对于靶向病变的位置，这些患者参加了一项 II 期试验。测量了消融区边缘和未消融肿瘤的体积，以确定是否实现了对每个肿瘤的完全覆盖，这将被认为是一次临床成功的消融。
每位患者在术前 2-3 个月接受了术前 mpMRI，并在 3T T2 加权轴向图像上手动勾画前列腺和病变。在手术中立即进行术后 1.5T T1 加权增强轴向图像后，还手动勾画了前列腺和消融区。使用初始仿射配准和前列腺表面的非刚性薄板样条配准，将病变表面非刚性地配准到术后图像上。使用射线的均匀球形分布计算注册病变和消融区之间的边界，并计算相交的体积。对每个前列腺进行五次轮廓勾画，以确定勾画的可变性及其对病变和消融区相交的影响。
我们的研究表明，分割的肿瘤和消融区的边界是接近的。在分析的 23 个病变中，有 11 个完全被消融区覆盖，12 个部分被覆盖。如果针移动 1.0、2.0 和 2.6mm，则分别会有 19、21 和所有肿瘤完全被消融区覆盖。所有肿瘤的未消融肿瘤体积中位数为 0.1，IQR 为 3.7，占肿瘤体积中位数的 0.2%（46.5，IQR 为 46.3）。在部分消融的病例中，肿瘤超出消融区的延伸中位数为 0.9mm（IQR 为 1.3mm），最远的肿瘤延伸 2.6mm。
在所有情况下，肿瘤边界都接近消融区边界，在某些情况下，消融区边界并没有完全包围肿瘤。我们的结果表明，有些消融并不完全成功，需要更准确的针跟踪和引导方法。研究的局限性包括所使用的配准和分割方法的误差，以及注册的 T2 和 T1 MRI 序列之间的不同体素大小和对比度以及前列腺术后的不对称肿胀。
