Abstract
BackgroundFor yttrium-90 (90Y) 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 (99mTc) macroaggregated albumin (MAA) single photon emission computed tomography with integrated CT (SPECT/CT) of the lung as part of our routine dosimetric protocol for 90Y 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.MethodsThis is a retrospective study of our pulmonary clinical outcomes and comparison of lung dosimetric accuracy and precision by 99mTc MAA SPECT/CT versus conventional planar methodology. 90Y 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.ResultsThirty 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 99mTc 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 99mTc MAA SPECT/CT and planar methodology are both accurate (bias <0.5 Gy), but 99mTc 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.ConclusionsPersonalized predictive lung dosimetry by 99mTc MAA SPECT/CT is clinically feasible, safe, and more precise than conventional planar methodology for 90Y radioembolization radiation planning.
Highlights
For yttrium-90 (90Y) 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
For 90Y resin microspheres, the ‘partition model’ is the simplest method of predictive dosimetry to personalize the intended radiation absorbed doses to tumor and non-tumorous liver and lung based on 99mTc macroaggregated albumin (MAA) scintigraphy [6,7]
We previously showed that 99mTc MAA single photon emission computed tomography with integrated CT (SPECT/CT) of the liver can improve the safety and effectiveness of 90Y resin microsphere RE [12]
Summary
For yttrium-90 (90Y) 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. For 90Y resin microspheres, the ‘partition model’ is the simplest method of predictive dosimetry to personalize the intended radiation absorbed doses to tumor and non-tumorous liver and lung based on 99mTc macroaggregated albumin (MAA) scintigraphy [6,7]. A standard mass of 1,000 g is often assumed [8] - an assumption which risks under- or overestimation of the lung radiation absorbed dose depending on patient size, pre-existing chronic lung disease, prior lung surgery or irradiation, lung shunt fraction (LSF), or injected 90Y activity. In the modern era of personalized medicine, there is a clinical need to shift away from assumed masses and to embrace patient-specific lung mass estimates for predictive dosimetry in 90Y RE
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