Stella M, Braat Ajat, Lam Mgeh, de Jong Hwam, van Rooij R
Department of Radiology and Nuclear Medicine, University Medical Center, Utrecht, Heidelberglaan 100, 3584, CX, Utrecht, The Netherlands.
EJNMMI Phys. 2020 Jul 14;7(1):48. doi: 10.1186/s40658-020-00317-8.
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 (Ho)-microspheres, and technetium-99 m (Tc)-colloid was developed: Ho-microspheres used as scout and therapeutic particles, and Tc-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 Tc downscatter on Ho dosimetry, by comparing Ho-SPECT reconstructions of patient scans acquired before (Ho-only) and after additional administration of Tc-colloid (Ho-DI).
The Ho-only and Ho-DI scans were performed in short succession by injecting Tc-colloid on the scanner table. To compensate for Tc 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, VOI, and VOI were manually delineated on the Ho-only reconstruction and transferred to the co-registered Ho-DI reconstruction. Absorbed dose within the resulting VOIs, and in the lungs (VOI), was calculated based on the administered therapeutic activity.
The qualitative assessment showed no distinct clinical preference for either Ho-only or Ho-DI SPECT (kappa = 0.093). Quantitative analysis indicated that the mean absorbed dose difference between Ho-DI and Ho-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 VOI VOI and VOI, respectively. The corresponding Pearson's correlation coefficient between Ho-only and Ho-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.
精确的剂量测定在放射性栓塞治疗中至关重要。为此，我们开发了一种基于双同位素（DI）单光子发射计算机断层扫描（SPECT）成像的健康肝脏剂量测定自动方案，该方案结合了钬 - 166（Ho）微球和锝 - 99m（Tc）胶体：Ho微球用作定位和治疗粒子，Tc胶体用于识别健康肝脏。DI SPECT能够自动且准确地估计吸收剂量，实现真正的个性化剂量测定。然而，同位素之间的光子串扰可能会影响图像质量。本研究通过比较患者在额外注射Tc胶体之前（仅Ho）和之后（Ho - DI）获得的扫描图像的Ho - SPECT重建，来研究Tc散射对Ho剂量测定的影响。
通过在扫描台上注射Tc胶体，相继进行仅Ho和Ho - DI扫描。为补偿Tc散射，在DI图像重建中使用基于能量窗的散射校正方法来考虑其影响。由两名核医学医师进行独立的盲法比较，对65对SPECT/CT进行定性评估。观察者间的一致性通过Cohen卡方系数进行测试。对于定量分析，在仅Ho重建图像上手动勾勒出肝脏内的两个感兴趣体积VOI和VOI，并将其转移到配准后的Ho - DI重建图像上。根据给予的治疗活度计算所得VOI以及肺部（VOI）内的吸收剂量。
定性评估显示，对于仅Ho或Ho - DI SPECT，没有明显的临床偏好（卡方 = 0.093）。定量分析表明，对于VOI、VOI和VOI，Ho - DI与仅Ho之间的平均吸收剂量差异分别为 - 2.00 ± 2.84 Gy（中位数27 Gy；p值 < 0.00001）、 - 5.27 ± （此处原文可能有误，推测为8.99）8.99 Gy（中位数116 Gy；p值 = 0.00035）和0.80 ± 1.08 Gy（中位数3 Gy；p值 < 0.00001）。仅Ho和Ho - DI之间吸收剂量的相应Pearson相关系数分别为0.97、0.99和0.82。
DI方案能够实现自动剂量测定，且图像质量和准确性不受影响。
上述临床研究于2014年2月20日在Clinicaltrials.gov注册（NCT02067988）。
