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通过 Pb 光子发射实现 Ra α 粒子治疗的优化 SPECT 成像。

Optimized SPECT Imaging of Ra α-Particle Therapy by Pb Photon Emissions.

机构信息

Division of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway;

Department of Life Sciences and Health, Oslo Metropolitan University, Oslo, Norway.

出版信息

J Nucl Med. 2023 Jul;64(7):1131-1137. doi: 10.2967/jnumed.122.264455. Epub 2023 Jun 2.

Abstract

In preparation for an α-particle therapy trial using 1-7 MBq of Ra, the feasibility of tomographic SPECT/CT imaging was of interest. The nuclide decays in 6 steps to stable Pb, with Pb as the principle photon-emitting nuclide. Bi and Tl emit high-energy photons up to 2,615 keV. A phantom study was conducted to determine the optimal acquisition and reconstruction protocol. The spheres of a body phantom were filled with a Ra-RaCl solution, and the background compartment was filled with water. Images were acquired on a SPECT/CT system. In addition, 30-min scans were acquired for 80- and 240-keV emissions, using triple-energy windows, with both medium-energy and high-energy collimators. Images were acquired at 90-95 and 29-30 kBq/mL, plus an explorative 3-min acquisition at 20 kBq/mL (using only the optimal protocol). Reconstructions were performed with attenuation correction only, attenuation plus scatter correction, 3 levels of postfiltering, and 24 levels of iterative updates. Acquisitions and reconstructions were compared using the maximum value and signal-to-scatter peak ratio for each sphere. Monte Carlo simulations were performed to examine the contributions of key emissions. Secondary photons of the 2,615-keV Tl emission produced in the collimators make up most of the acquired energy spectrum, as revealed by Monte Carlo simulations, with only a small fraction (3%-6%) of photons in each window providing useful information for imaging. Still, decent image quality is possible at 30 kBq/mL, and nuclide concentrations are imageable down to approximately 2-5 kBq/mL. The overall best results were obtained with the 240-keV window, medium-energy collimator, attenuation and scatter correction, 30 iterations and 2 subsets, and a 12-mm gaussian postprocessing filter. However, all combinations of the applied collimators and energy windows were capable of producing adequate results, even though some failed to reconstruct the 2 smallest spheres. SPECT/CT imaging of Ra in equilibrium with daughters is possible, with sufficient image quality to provide clinical utility for the current trial of intraperitoneally administrated activity. A systematic scheme for optimization was designed to select acquisition and reconstruction settings.

摘要

为了准备使用 1-7MBq 的 Ra 进行 α 粒子治疗试验,我们对断层 SPECT/CT 成像的可行性很感兴趣。该核素通过 6 步衰变为稳定的 Pb,其中 Pb 是主要的光子发射核素。Bi 和 Tl 发射高达 2615keV 的高能光子。我们进行了一项体模研究来确定最佳的采集和重建方案。将一个体模的球体充满 Ra-RaCl 溶液,背景腔充满水。在 SPECT/CT 系统上采集图像。此外,使用三重能窗,采集 80keV 和 240keV 发射的 30 分钟扫描,使用中能和高能准直器。以 90-95 和 29-30kBq/mL 采集图像,并在 20kBq/mL 时进行探索性 3 分钟采集(仅使用最佳方案)。仅使用最佳方案)。使用每个球体的最大值和信号与散射峰比来比较采集和重建。使用 Monte Carlo 模拟来检查关键发射的贡献。正如 Monte Carlo 模拟所揭示的那样,在准直器中产生的 2615keV Tl 发射的二次光子构成了采集能谱的大部分,每个窗口中只有一小部分(3%-6%)光子提供有用的成像信息。尽管如此,在 30kBq/mL 时仍可以获得良好的图像质量,并且可以成像的核素浓度低至约 2-5kBq/mL。在 30 次迭代和 2 个子集中,使用 240keV 窗口、中能准直器、衰减和散射校正、12mm 高斯后处理滤波器获得了最佳的整体结果。然而,即使有些无法重建最小的 2 个球体,应用的准直器和能窗的所有组合都能够产生足够的结果。使用与子体处于平衡状态的 Ra 的 SPECT/CT 成像成为可能,并且具有足够的图像质量为当前腹膜内给予活性的试验提供临床应用。设计了一个系统的优化方案来选择采集和重建设置。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/518f/10315694/110777821982/jnumed.122.264455absf1.jpg

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