Saleh Ziad, Thor Maria, Apte Aditya P, Sharp Gregory, Tang Xiaoli, Veeraraghavan Harini, Muren Ludvig, Deasy Joseph
Department of Medical Physics, Memorial Sloan Kettering Cancer Center, 1275 York Ave., New York, NY 10065, USA.
Phys Med Biol. 2016 Aug 21;61(16):6172-80. doi: 10.1088/0031-9155/61/16/6172. Epub 2016 Jul 29.
Deformable image registration (DIR) is essential for adaptive radiotherapy (RT) for tumor sites subject to motion, changes in tumor volume, as well as changes in patient normal anatomy due to weight loss. Several methods have been published to evaluate DIR-related uncertainties but they are not widely adopted. The aim of this study was, therefore, to evaluate intra-patient DIR for two highly deformable organs-the bladder and the rectum-in prostate cancer RT using a quantitative metric based on multiple image registration, the distance discordance metric (DDM). Voxel-by-voxel DIR uncertainties of the bladder and rectum were evaluated using DDM on weekly CT scans of 38 subjects previously treated with RT for prostate cancer (six scans/subject). The DDM was obtained from group-wise B-spline registration of each patient's collection of repeat CT scans. For each structure, registration uncertainties were derived from DDM-related metrics. In addition, five other quantitative measures, including inverse consistency error (ICE), transitivity error (TE), Dice similarity (DSC) and volume ratios between corresponding structures from pre- and post- registered images were computed and compared with the DDM. The DDM varied across subjects and structures; DDMmean of the bladder ranged from 2 to 13 mm and from 1 to 11 mm for the rectum. There was a high correlation between DDMmean of the bladder and the rectum (Pearson's correlation coefficient, R p = 0.62). The correlation between DDMmean and the volume ratios post-DIR was stronger (R p = 0.51; 0.68) than the correlation with the TE (bladder: R p = 0.46; rectum: R p = 0.47), or the ICE (bladder: R p = 0.34; rectum: R p = 0.37). There was a negative correlation between DSC and DDMmean of both the bladder (R p = -0.23) and the rectum (R p = -0.63). The DDM uncertainty metric indicated considerable DIR variability across subjects and structures. Our results show a stronger correlation with volume ratios and with the DSC using DDM compared to using ICE and TE. The DDM has the potential to quantitatively identify regions of large DIR uncertainties and consequently identify anatomical/scan outliers. The DDM can, thus, be applied to improve the adaptive RT process for tumor sites subject to motion.
对于因运动、肿瘤体积变化以及体重减轻导致患者正常解剖结构改变的肿瘤部位，可变形图像配准（DIR）对于自适应放射治疗（RT）至关重要。已经发表了几种方法来评估与DIR相关的不确定性，但它们并未被广泛采用。因此，本研究的目的是使用基于多图像配准的定量指标——距离不一致性指标（DDM），评估前列腺癌放疗中两个高度可变形器官（膀胱和直肠）的患者体内DIR。使用DDM在38例先前接受前列腺癌放疗的受试者（每位受试者6次扫描）的每周CT扫描上评估膀胱和直肠的逐体素DIR不确定性。DDM是从每位患者的重复CT扫描集合的组间B样条配准中获得的。对于每个结构，配准不确定性是从与DDM相关的指标中得出的。此外，还计算了其他五个定量指标，包括反向一致性误差（ICE）、传递性误差（TE）、骰子相似性（DSC）以及配准前后相应结构之间的体积比，并与DDM进行比较。DDM因受试者和结构而异；膀胱的DDM平均值范围为2至13毫米，直肠为1至11毫米。膀胱和直肠的DDM平均值之间存在高度相关性（皮尔逊相关系数，Rp = 0.62）。DDM平均值与DIR后体积比之间的相关性（Rp = 0.51；0.68）比与TE（膀胱：Rp = 0.46；直肠：Rp = 0.47）或ICE（膀胱：Rp = 0.34；直肠：Rp = 0.37）的相关性更强。膀胱和直肠的DSC与DDM平均值之间均存在负相关性（膀胱：Rp = -0.23；直肠：Rp = -0.63）。DDM不确定性指标表明受试者和结构之间的DIR存在相当大的变异性。我们的结果表明，与使用ICE和TE相比，使用DDM时与体积比和DSC的相关性更强。DDM有可能定量识别DIR不确定性较大的区域，从而识别解剖学/扫描异常值。因此，DDM可用于改善受运动影响的肿瘤部位的自适应放疗过程。
