He Bin, Du Yong, Segars W Paul, Wahl Richard L, Sgouros George, Jacene Heather, Frey Eric C
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287-0859, USA.
Med Phys. 2009 Feb;36(2):612-9. doi: 10.1118/1.3063156.
Estimating organ residence times is an essential part of patient-specific dosimetry for radioimmunotherapy (RIT). Quantitative imaging methods for RIT are often evaluated using a single physical or simulated phantom but are intended to be applied clinically where there is variability in patient anatomy, biodistribution, and biokinetics. To provide a more relevant evaluation, the authors have thus developed a population of phantoms with realistic variations in these factors and applied it to the evaluation of quantitative imaging methods both to find the best method and to demonstrate the effects of these variations. Using whole body scans and SPECT/CT images, organ shapes and time-activity curves of 111In ibritumomab tiuxetan were measured in dosimetrically important organs in seven patients undergoing a high dose therapy regimen. Based on these measurements, we created a 3D NURBS-based cardiac-torso (NCAT)-based phantom population. SPECT and planar data at realistic count levels were then simulated using previously validated Monte Carlo simulation tools. The projections from the population were used to evaluate the accuracy and variation in accuracy of residence time estimation methods that used a time series of SPECT and planar scans, Quantitative SPECT (QSPECT) reconstruction methods were used that compensated for attenuation, scatter, and the collimator-detector response. Planar images were processed with a conventional (CPlanar) method that used geometric mean attenuation and triple-energy window scatter compensation and a quantitative planar (QPlanar) processing method that used model-based compensation for image degrading effects. Residence times were estimated from activity estimates made at each of five time points. The authors also evaluated hybrid methods that used CPlanar or QPlanar time-activity curves rescaled to the activity estimated from a single QSPECT image. The methods were evaluated in terms of mean relative error and standard deviation of the relative error in the residence time estimates taken over the phantom population. The mean errors in the residence time estimates over all the organs were < 9.9% (pure QSPECT), < 13.2% (pure QPLanar), < 7.2% (hybrid QPlanar/QSPECT), < 19.2% (hybrid CPlanar/QSPECT), and 7%-159% (pure CPlanar). The standard deviations of the errors for all the organs over all the phantoms were < 9.9%, < 11.9%, < 10.8%, < 22.0%, and < 107.9% for the same methods, respectively. The processing methods differed both in terms of their average accuracy and the variation of the accuracy over the population of phantoms, thus demonstrating the importance of using a phantom population in evaluating quantitative imaging methods. Hybrid CPlanar/QSPECT provided improved accuracy compared to pure CPlanar and required the addition of only a single SPECT acquisition. The QPlanar or hybrid QPlanar/QSPECT methods had mean errors and standard deviations of errors that approached those of pure QSPECT while providing simplified image acquisition protocols, and thus may be more clinically practical.
估算器官驻留时间是放射免疫疗法（RIT）中患者特异性剂量测定的重要组成部分。RIT的定量成像方法通常使用单个物理或模拟体模进行评估，但旨在应用于患者解剖结构、生物分布和生物动力学存在差异的临床环境。为了提供更相关的评估，作者因此开发了一组在这些因素上具有实际变化的体模，并将其应用于定量成像方法的评估，以找到最佳方法并证明这些变化的影响。使用全身扫描和SPECT/CT图像，在接受高剂量治疗方案的7名患者的剂量学重要器官中测量了111In 替伊莫单抗的器官形状和时间-活度曲线。基于这些测量，我们创建了一个基于3D NURBS的心脏-躯干（NCAT）体模群体。然后使用先前经过验证的蒙特卡罗模拟工具在实际计数水平上模拟SPECT和平面数据。该群体的投影用于评估使用SPECT和平面扫描时间序列的驻留时间估计方法的准确性和准确性变化，使用了补偿衰减、散射和准直器-探测器响应的定量SPECT（QSPECT）重建方法。平面图像使用传统的（CPlanar）方法进行处理，该方法使用几何平均衰减和三能量窗散射补偿，以及使用基于模型的图像退化效应补偿的定量平面（QPlanar）处理方法。从五个时间点的每个时间点的活度估计值中估计驻留时间。作者还评估了混合方法，这些方法使用重新缩放至从单个QSPECT图像估计的活度的CPlanar或QPlanar时间-活度曲线。根据体模群体中驻留时间估计的平均相对误差和相对误差的标准偏差对这些方法进行评估。所有器官驻留时间估计的平均误差在纯QSPECT时<9.9%，纯QPLanar时<13.2%，混合QPlanar/QSPECT时<7.2%，混合CPlanar/QSPECT时<19.2%，纯CPlanar时为7%-159%。对于相同的方法，所有体模上所有器官误差的标准偏差分别<9.9%、<11.9%、<10.8%、<22.0%和<107.9%。这些处理方法在平均准确性和体模群体中准确性的变化方面都有所不同，从而证明了在评估定量成像方法时使用体模群体的重要性。与纯CPlanar相比，混合CPlanar/QSPECT提高了准确性，并且只需要额外进行一次SPECT采集。QPlanar或混合QPlanar/QSPECT方法的平均误差和误差标准偏差接近纯QSPECT，同时提供了简化的图像采集方案，因此可能在临床上更实用。
