背景:经动脉放射栓塞的发展导致了载有钬-166(166Ho)的新型微球的概念。然而,由于166Ho单光子发射计算机断层扫描(SPECT)中散射分量的复杂性,关于图像质量和剂量学的问题正在出现。这项工作的目的是研究散射分量和校正方法,以提出合适的解决方案,并评估对图像质量和剂量学的影响,包括蒙特卡罗(MC)模拟,幻影,和患者数据。
方法:为了散射校正的目的,研究了双能量窗(DEW)和三能量窗(TEW)方法,并使用对比恢复系数(CRC)和对比噪声比(CNR)进行了比较。首先,进行MC模拟以评估使用的能量窗口中的所有散射分量,还要确认DEW方法所需参数的选择。然后,在模拟理想散射校正的条件下进行了对Jaszczak体模的采集的MC模拟。可以重建这些模拟投影,并将其与通过两种方法校正的实际采集进行比较,然后重建。最后,两种方法均应用于患者数据,并评估其对个性化剂量学的影响.
结果:MC模拟证实了对DEW方法使用k=1。这些模拟还证实了主能量窗口中散射分量的复杂性,其中高能伽马射线分量约占检测到的总计数的一半,连同可忽略的X射线成分和可忽略的荧光存在。CRC和CNR分析,在模拟体模的无散射投影和相同体模的散射校正采集上实现,建议提高TEW方法的效率,即使在更高的噪音水平的价格。最后,这些方法,应用于患者数据,在非肿瘤肝脏吸收剂量方面表现出显著差异,50Gy以下的非肿瘤肝脏分数,肿瘤吸收剂量,和高于150Gy的肿瘤分数。
结论:本研究证明了散射校正对个性化剂量学对患者数据的影响。提出了使用TEW方法进行166HoSPECT成像中的散射校正。
BACKGROUND: Developments in transarterial radioembolization led to the conception of new microspheres loaded with holmium-166 (166Ho). However, due to the complexity of the scatter components in 166Ho single photon emission computed tomography (SPECT), questions about image quality and dosimetry are emerging. The aims of this work are to investigate the scatter components and correction methods to propose a suitable solution, and to evaluate the impact on image quality and dosimetry including Monte-Carlo (MC) simulations, phantom, and patient data.
METHODS: Dual energy window (DEW) and triple energy window (TEW) methods were investigated for scatter correction purposes and compared using Contrast Recovery Coefficients (CRC) and Contrast to Noise Ratios (CNR). First, MC simulations were carried out to assess all the scatter components in the energy windows used, also to confirm the choice of the parameter needed for the DEW method. Then, MC simulations of acquisitions of a Jaszczak phantom were conducted with conditions mimicking an ideal scatter correction. These simulated projections can be reconstructed and compared with real acquisitions corrected by both methods and then reconstructed. Finally, both methods were applied on patient data and their impact on personalized dosimetry was evaluated.
RESULTS: MC simulations confirmed the use of k = 1 for the DEW method. These simulations also confirmed the complexity of scatter components in the main energy window used with a high energy gamma rays component of about half of the total counts detected, together with a negligible X rays component and a negligible presence of fluorescence. CRC and CNR analyses, realized on simulated scatter-free projections of the phantom and on scatter corrected acquisitions of the same phantom, suggested an increased efficiency of the TEW method, even at the price of higher level of noise. Finally, these methods, applied on patient data, showed significant differences in terms of non-tumoral liver absorbed dose, non-tumoral liver fraction under 50 Gy, tumor absorbed dose, and tumor fraction above 150 Gy.
CONCLUSIONS: This study demonstrated the impact of scatter correction on personalized dosimetry on patient data. The use of a TEW method is proposed for scatter correction in 166Ho SPECT imaging.