Personalized predictive lung dosimetry by technetium-99m macroaggregated albumin SPECT/CT for yttrium-90 radioembolization

Background: For yttrium-90 (Y-90) radioembolization, the common practice of assuming a standard 1,000-g lung mass for predictive dosimetry is fundamentally incongruent with the modern philosophy of personalized medicine. We recently developed a technique of personalized predictive lung dosimetry using technetium-99m (Tc-99m) macroaggregated albumin (MAA) single photon emission computed tomography with integrated CT (SPECT/CT) of the lung as part of our routine dosimetric protocol for Y-90 radioembolization. Its rationales are the technical superiority of SPECT/CT over planar scintigraphy, ease and convenience of lung auto-segmentation CT densitovolumetry, and dosimetric advantage of patient-specific lung parenchyma masses. Methods: This is a retrospective study of our pulmonary clinical outcomes and comparison of lung dosimetric accuracy and precision by Tc-99m MAA SPECT/CT versus conventional planar methodology. Y-90 resin microspheres (SIR-Spheres) were used for radioembolization. Diagnostic CT densitovolumetry was used as a reference for lung parenchyma mass. Pulmonary outcomes were based on follow-up diagnostic CT chest or X-ray. Results: Thirty patients were analyzed. The mean lung parenchyma mass of our Southeast Asian cohort was 822 +/- 103 g standard deviation (95% confidence interval 785 to 859 g). Patient-specific lung parenchyma mass estimation by CT densitovolumetry on Tc-99m MAA SPECT/CT is accurate (bias -21.7 g) and moderately precise (95% limits of agreement -194.6 to +151.2 g). Lung mean radiation absorbed doses calculated by Tc-99m MAA SPECT/CT and planar methodology are both accurate (bias <0.5 Gy), but Tc-99m MAA SPECT/CT offers better precision over planar methodology (95% limits of agreement -1.76 to +2.40 Gy versus -3.48 to +3.31 Gy, respectively). None developed radiomicrosphere pneumonitis when treated up to a lung mean radiation absorbed dose of 18 Gy at a median follow-up of 4.4 months. Conclusions: Personalized predictive lung dosimetry by Tc-99m MAA SPECT/CT is clinically feasible, safe, and more precise than conventional planar methodology for Y-90 radioembolization radiation planning.