PT - JOURNAL ARTICLE AU - Martina Stella AU - Arthur J.A.T. Braat AU - Marnix G.E.H. Lam AU - Hugo W.A.M. de Jong AU - Rob van Rooij TI - Clinical feasibility of quantitative holmium-166 SPECT in presence of technetium-99m colloid DP - 2020 May 01 TA - Journal of Nuclear Medicine PG - 569--569 VI - 61 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/61/supplement_1/569.short 4100 - http://jnm.snmjournals.org/content/61/supplement_1/569.full SO - J Nucl Med2020 May 01; 61 AB - 569Objectives: Investigate the effect of technetium-99m colloid (99mTc) photons crosstalk on holmium-166 (166Ho) dosimetry when used in combination to perform dual isotope (DI) SPECT imaging. This protocol, using 166Ho-microspheres and 99mTc to identify the healthy liver, allows for automatic compartmental dosimetry before and after radioembolization treatment. Methods: To assess the crosstalk (the reciprocal influence of one isotope’s downscatter in the other’s main photopeak), 166Ho-SPECT reconstructions of patient scans acquired before and after additional 99mTc administration (referred to as 166Ho-only and 166Ho-DI respectively) were compared. The 166Ho-only and 166Ho-DI SPECT scans were performed with <10 min interval to minimize patient motion. Images were reconstructed using Siemens Symbia software (Flash3D). To compensate for 99mTc-photons crosstalk, its influence in the 166Ho photopeak (81 keV) window was accounted for in the DI image reconstruction using energy window based scatter correction methods. The quality of the 166Ho-DI image was compared to that of the 166Ho-only image, qualitatively and quantitatively. The qualitative assessment was performed by independent blinded comparison by two nuclear medicine physicians assessing 65 pairs of SPECT/CT scans. Inter-observer agreement was tested by Cohen's kappa coefficient. For the quantitative analysis, three volumes of interest (VOI) were considered. VOITUMOR and VOIHEALTHY, within the liver, were manually delineated on the 166Ho-only reconstruction and transferred to the co-registered 166Ho-DI reconstruction. VOILUNGS was semi-automatically segmented in both 166Ho-only and 166Ho-DI reconstructions. Absorbed dose within the resulting VOIs was calculated based on the administered therapeutic activity. Results: The qualitative assessment showed no distinct preference for either the 166Ho-only or 166Ho-DI SPECT (kappa = 0.093). Quantitative analysis indicated that the median absorbed dose in the VOIs was 27, 116 and 3 Gy for VOIHEALTHY, VOITUMOR and VOILUNGS, the mean difference in absorbed dose between 166Ho-DI and 166Ho-only was -2.00±2.84 Gy, -5.27±8.99 Gy and 0.80±1.08 Gy respectively. These differences were regarded as clinically not relevant by treating physicians. The corresponding Pearson’s correlation coefficient between 166Ho-only and 166Ho-DI for absorbed dose was 0.97, 0.99 and 0.82 for VOIHEALTHY, VOITUMOR and VOILUNGS. Conclusions: The DI protocol enables satisfying 166Ho SPECT within the clinical reconstruction framework, allowing an automatic estimation of absorbed dose in tumors, healthy liver and lungs. Research Support: Nederlandse Organisatie voor Wetenschappelijk Onderzoek