Accurate dosimetry is essential in radioembolization. To this purpose, an automatic protocol for healthy liver dosimetry based on dual isotope (DI) SPECT imaging, combining holmium-166 (166Ho)-microspheres, and technetium-99 m (99mTc)-colloid was developed: 166Ho-microspheres used as scout and therapeutic particles, and 99mTc-colloid to identify the healthy liver. DI SPECT allows for an automatic and accurate estimation of absorbed doses, introducing true personalized dosimetry. However, photon crosstalk between isotopes can compromise image quality. This study investigates the effect of 99mTc downscatter on 166Ho dosimetry, by comparing 166Ho-SPECT reconstructions of patient scans acquired before (166Ho-only) and after additional administration of 99mTc-colloid (166Ho-DI). The 166Ho-only and 166Ho-DI scans were performed in short succession by injecting 99mTc-colloid on the scanner table. To compensate for 99mTc downscatter, its influence was accounted for in the DI image reconstruction using energy window-based scatter correction methods. The qualitative assessment was performed by independent blinded comparison by two nuclear medicine physicians assessing 65 pairs of SPECT/CT. Inter-observer agreement was tested by Cohen’s kappa coefficient. For the quantitative analysis, two volumes of interest within the liver, VOITUMOR, and VOIHEALTHY were manually delineated on the 166Ho-only reconstruction and transferred to the co-registered 166Ho-DI reconstruction. Absorbed dose within the resulting VOIs, and in the lungs (VOILUNGS), was calculated based on the administered therapeutic activity. The qualitative assessment showed no distinct clinical preference for either 166Ho-only or 166Ho-DI SPECT (kappa = 0.093). Quantitative analysis indicated that the mean absorbed dose difference between 166Ho-DI and 166Ho-only was − 2.00 ± 2.84 Gy (median 27 Gy; p value < 0.00001), − 5.27 ± 8.99 Gy (median 116 Gy; p value = 0.00035), and 0.80 ± 1.08 Gy (median 3 Gy; p value < 0.00001) for VOIHEALTHY, VOITUMOR, and VOILUNGS, respectively. The corresponding Pearson’s correlation coefficient between 166Ho-only and 166Ho-DI for absorbed dose was 0.97, 0.99, and 0.82, respectively. The DI protocol enables automatic dosimetry with undiminished image quality and accuracy. The clinical study mentioned is registered with Clinicaltrials.gov (NCT02067988) on 20 February 2014.

中文翻译：

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使用 99mTc 胶体从双同位素采集中获得的定量 166Ho 微球 SPECT 在临床上是可行的。

准确的剂量测定在放射栓塞术中至关重要。为此，开发了一种基于双同位素 (DI) SPECT 成像的健康肝脏剂量测定自动协议，结合了钬 166 (166Ho)-微球和锝-99 m (99mTc)-胶体：166Ho-微球用作侦察和治疗颗粒，以及 99mTc-胶体来识别健康的肝脏。DI SPECT 允许自动和准确地估计吸收剂量，引入真正的个性化剂量测定。然而，同位素之间的光子串扰会影响图像质量。本研究通过比较在额外施用 99mTc-胶体 (166Ho-DI) 之前（仅 166Ho）和之后获得的患者扫描的 166Ho-SPECT 重建，研究了 99mTc 向下散射对 166Ho 剂量测定的影响。通过在扫描台上注入 99mTc 胶体，连续进行 166Ho-only 和 166Ho-DI 扫描。为了补偿 99mTc 向下散射，在使用基于能量窗口的散射校正方法进行 DI 图像重建时考虑了其影响。由两名核医学医师评估 65 对 SPECT/CT，通过独立盲法比较进行定性评估。通过 Cohen 的 kappa 系数检验观察者间的一致性。对于定量分析，肝脏内的两个感兴趣的体积，VOITUMOR 和 VOIHEALTHY 在仅 166Ho 重建上手动描绘，并转移到共同注册的 166Ho-DI 重建。根据给药的治疗活性计算得到的 VOI 和肺 (VOILUNGS) 内的吸收剂量。定性评估显示对仅 166Ho 或 166Ho-DI SPECT 没有明显的临床偏好（kappa = 0.093）。定量分析表明，166Ho-DI 和仅 166Ho 之间的平均吸收剂量差异为 - 2.00 ± 2.84 Gy（中位数 27 Gy；p 值 < 0.00001），- 5.27 ± 8.99 Gy（中位数 116 Gy；p 值 = 0.00035）， VOIHEALTHY、VOITUMOR 和 VOILUNGS 分别为 0.80 ± 1.08 Gy（中位数 3 Gy；p 值 < 0.00001）。166Ho-only 和 166Ho-DI 吸收剂量的相应 Pearson 相关系数分别为 0.97、0.99 和 0.82。DI 协议可实现图像质量和准确性不降低的自动剂量测定。提到的临床研究已于 2014 年 2 月 20 日在 Clinicaltrials.gov (NCT02067988) 注册。