Intrahepatic dosimetry is paramount to optimize radioembolization treatment accuracy using radioactive holmium-166 microspheres (166Ho). This requires a practical protocol that combines quantitative imaging of microsphere distribution with automated and robust delineation of the volumes of interest. To this end, we propose a dual isotope single photon emission computed tomography (SPECT) protocol based on 166Ho therapeutic microspheres and technetium-99 m (99mTc) stannous phytate, which accumulates in healthy liver tissue. This protocol may allow accurate and automatic estimation of tumor-absorbed dose and healthy liver-absorbed dose. The current study focuses on a Monte Carlo-based reconstruction framework that inherently corrects for scatter crosstalk between the 166Ho and 99mTc imaging. To demonstrate the feasibility of the method, it is evaluated with realistic phantom experiments and patient data. The Utrecht Monte Carlo System (UMCS) was extended to include detailed modeling of crosstalk interactions between 99mTc and 166Ho. First, 99mTc images were reconstructed including energy window-based corrections for 166Ho downscatter. Next, 99mTc downscatter in the 81-keV 166Ho window was Monte Carlo simulated to allow quantitative reconstruction of the 166Ho images. The accuracy of the 99mTc-downscatter modeling was evaluated by comparing measurements with simulations. In addition, the ratio between 99mTc and 166Ho yielding the best 166Ho dose estimates was established and the quantitative accuracy was reported. Given the same level of activity, 99mTc contributes twice as many counts to the 81-keV window than 166Ho, and four times as many counts to the 140-keV window, applying a 166Ho/99mTc ratio of 5:1 yielded a high accuracy in both 166Ho and 99mTc reconstruction. Phantom experiments revealed that the accuracy of quantitative 166Ho activity recovery was reduced by 10% due to the presence of 99mTc. Twenty iterations (8 subsets) of the SPECT/CT reconstructions were considered feasible for clinical practice. Applicability of the proposed protocol was shown in a proof-of-concept case. A novel 166Ho/99mTc dual-isotope protocol for automatic dosimetry compensates accurately for downscatter and allows for the addition of 99mTc without compromising 166Ho SPECT image quality.

中文翻译：

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同时¹⁶⁶何/ ^99米锝双同位素SPECT有用于radioembolization自动肝剂量基于蒙特卡罗downscatter校正

肝内剂量测定对于使用放射性166微球（166Ho）优化放射栓塞治疗的准确性至关重要。这需要一个实用的协议，该协议将微球分布的定量成像与感兴趣的体积的自动且可靠的描绘结合在一起。为此，我们提出了一种基于166Ho治疗性微球和m 99 m（99mTc）植酸亚锡的双同位素单光子发射计算机断层扫描（SPECT）协议，该协议积累在健康的肝脏组织中。该协议可以允许准确，自动地估计肿瘤吸收剂量和健康肝脏吸收剂量。当前的研究集中在基于蒙特卡洛的重建框架上，该框架可固有地校正166Ho和99mTc成像之间的散射串扰。为了证明该方法的可行性，它通过真实的幻像实验和患者数据进行评估。Utrecht蒙特卡洛系统（UMCS）已扩展为包括99mTc与166Ho之间的串扰相互作用的详细建模。首先，重建了99mTc图像，包括针对166Ho向下散射的基于能量窗口的校正。接下来，蒙特卡洛模拟了81keV 166Ho窗口中的99mTc向下散射，从而可以定量重建166Ho图像。通过将测量结果与仿真结果进行比较，评估了99mTc向下散射模型的准确性。此外，建立了99mTc与166Ho之间的比率，得出最佳的166Ho剂量估计值，并报道了定量准确性。在相同的活动水平下，99mTc对81-keV窗口的计数是166Ho的两倍，而对140keV窗口的计数是四倍，166Ho / 99mTc比例为5：1时，在166Ho和99mTc重构中都具有很高的准确性。虚拟实验表明，由于存在99mTc，定量166Ho活性回收的准确性降低了10％。SPECT / CT重建的二十次迭代（8个子集）被认为可用于临床实践。在概念证明的情况下，表明了所提出协议的适用性。用于自动剂量测定的新型166Ho / 99mTc双同位素协议可精确补偿向下散射，并允许添加99mTc，而不会影响166Ho SPECT图像质量。SPECT / CT重建的二十次迭代（8个子集）被认为可用于临床实践。在概念证明的情况下，表明了所提出协议的适用性。用于自动剂量测定的新型166Ho / 99mTc双同位素协议可精确补偿向下散射，并允许添加99mTc，而不会影响166Ho SPECT图像质量。SPECT / CT重建的二十次迭代（8个子集）被认为可用于临床实践。在概念证明的情况下，表明了所提出协议的适用性。用于自动剂量测定的新型166Ho / 99mTc双同位素协议可精确补偿向下散射，并允许添加99mTc，而不会影响166Ho SPECT图像质量。