Department of Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden.
Division of Oncology and Pathology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
Med Phys. 2018 Nov;45(11):5004-5018. doi: 10.1002/mp.13178. Epub 2018 Oct 8.
A hybrid planar-SPECT/CT method for tumor dosimetry in Lu-DOTATATE therapy, applicable to datasets consisting of multiple conjugate-view images and one SPECT/CT, is developed and evaluated.
The imaging protocol includes conjugate-view imaging at 1, 24, 96, and 168 h post infusion (p.i.) and a SPECT/CT acquisition 24 h p.i. The dosimetry method uses the planar images to estimate the shape of the time-activity concentration curve, which is then rescaled to absolute units using the SPECT-derived activity concentration. The resulting time-integrated activity concentration coefficient (TIACC) is used to calculate the tumor-absorbed dose. Semiautomatic segmentation techniques are applied for tumor delineation in both planar and SPECT images, where the planar image segmentation is accomplished using an active-rays-based technique. The selection of tumors is done by visual inspection of planar and SPECT images and applying a set of criteria concerning the tumor visibility and possible interference from superimposed activity uptakes in the planar images. Five different strategies for determining values from planar regions of interest (ROIs), based on entire or partial ROIs, and with and without background correction, are evaluated. Evaluation is performed against a SPECT/CT-based method on data from six patients where sequential conjugate-view and SPECT/CT imaging have been performed in parallel and against ground truths in Monte Carlo simulated images. The patient data are also used to evaluate the interoperator variability and to assess the validity of the developed criteria for tumor selection.
For patient images, the hybrid method produces TIACCs that are on average 6% below those of the SPECT/CT only method, with standard deviations for the relative TIACC differences of 8%-11%. Simulations show that the hybrid and SPECT-based methods estimate the TIACCs to within approximately 10% for tumors larger than around 10 ml, while for smaller tumors, all methods underestimate the TIACCs due to underestimations of the activity concentrations in the SPECT images. The planar image segmentation has a low operator dependence, with a median Dice similarity coefficient of 0.97 between operators. The adopted criteria for tumor selection manage to discriminate the tumors for which the absorbed-dose deviations between the hybrid and SPECT methods are the highest.
The hybrid method is found suitable for studies of tumor-absorbed doses in radionuclide therapy, provided that selection criteria regarding the visibility and overlapping activities in the planar images are applied.
开发并评估了一种适用于包含多个共轭视图图像和一个 SPECT/CT 的 Lu-DOTATATE 治疗肿瘤剂量学的混合平面 SPECT/CT 方法。
成像方案包括在注射后 1、24、96 和 168 小时进行共轭视图成像，以及在注射后 24 小时进行 SPECT/CT 采集。剂量测定方法使用平面图像估计时间-活性浓度曲线的形状，然后使用 SPECT 衍生的活性浓度对其进行缩放至绝对单位。由此产生的时间积分活性浓度系数（TIACC）用于计算肿瘤吸收剂量。半自动化分割技术应用于平面和 SPECT 图像中的肿瘤描绘，其中平面图像分割使用基于主动射线的技术完成。通过平面和 SPECT 图像的视觉检查以及应用一组关于肿瘤可见性和平面图像中重叠活性摄取可能干扰的标准来选择肿瘤。评估了基于平面感兴趣区域（ROI）的 5 种不同策略，这些策略基于整个或部分 ROI，以及是否带有和不带有背景校正。通过对来自 6 名患者的 SPECT/CT 数据的评估以及在蒙特卡罗模拟图像中的与地面真相进行比较，对该方法进行了评估。还使用患者数据评估操作员之间的可变性，并评估用于肿瘤选择的开发标准的有效性。
对于患者图像，混合方法产生的 TIACCs 平均比仅基于 SPECT/CT 的方法低 6%，相对 TIACC 差异的标准偏差为 8%-11%。模拟表明，混合和基于 SPECT 的方法对于大于约 10ml 的肿瘤，能够将 TIACCs 估计在大约 10%以内，而对于较小的肿瘤，由于 SPECT 图像中活性浓度的低估，所有方法都会低估 TIACCs。平面图像分割具有较低的操作员依赖性，操作员之间的中位数 Dice 相似系数为 0.97。采用的肿瘤选择标准设法区分了混合和 SPECT 方法之间吸收剂量偏差最高的肿瘤。
发现混合方法适用于放射性核素治疗中的肿瘤吸收剂量研究，前提是应用关于平面图像中可见性和重叠活动的选择标准。
