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SIR 2025

Interventional Oncology

Scientific Session

Session: Interventional Oncology - Y90 2

Optimizing 99cTcMAA Preparation For Y-90 Radioembolization Workup

Monday, March 31, 2025
3:36 PM – 3:45 PM CT
Location: Music City Center, 208 AB
Purpose: Physicians rely on tumor to normal ratio (TNR) and lung shunt fraction (LSF) derived from Technetium-99m macroaggregated albumin (Tc-MAA) uptake to determine optimal Y-90 dosage for each patient. Though there have been improvements in Tc-MAA imaging protocols, no studies have attempted to optimize Tc-MAA administration itself. Informal survey results indicate a lack of standardization in the method of Tc-MAA injection for Y-90 workup. This study evaluates preparation methods for Tc-MAA administration.

Materials and Methods: Two dilution methods for Tc-MAA administration were investigated: dilution of Tc-MAA into 2 ml of normal saline (NS) (Method 1) and into 20 ml of NS (Method 2). Five trials were conducted per method. In each trial, the prepared Tc-MAA was injected through a 0.21” ID microcatheter (MC) (Cook Medical, OH, USA), attached to a 3-way stopcock, in equal distribution between 4 vials. Then, the MC was flushed with 5ml NS into a 5th vial. The activity (MBq) of vials 1 to 5 was measured using a dose-calibrator, and static planar imaging was used to measure Counts within a defined ROI for each vial. All materials were individually placed in the dose-calibrator to assess residual activity for each trial. ANOVA and boxplots were used to present variability in activity in trials between the two methods. 

Results: There was a significant difference in the distribution of Mean (SD) Activity (MBq) between vials 1 through 4 in Method 1: 7.32 (1.77) vs. Method 2: 7.63 (1.03) (F=10.569, p< 0.01), as well as the distribution of Mean (SD) Counts between vials 1 through 4 in Method 1: 19,811 (4254) vs. Method 2: 20,331 (2245) (F = 12.157, p< 0.01). Boxplots show the distribution of Activity and Counts in Method 1 (trending down from vial 1 to 4 with significant activity in the flush) and Method 2 (consistent through vials 1 to 4 with minimal activity in the flush). There was a significant difference in Residual Activity (MBq) Mean (SD) between Method 1: 2.02 (0.436) and Method 2: 0.268 (0.399) (F value=43.9, p< 0.001).

Conclusion: These findings show less variability in activity during Tc-MAA administration with Method 2. Thus, dilution of Tc-MAA into 20ml NS may allow for more uniform administration compared to 2ml NS, improving TNR and LSF determination accuracy. As demonstrated in the boxplots, a higher concentration of MAA earlier in administration could result in flow dynamic changes and larger residual volumes due to stagnation. In-vivo and in-vitro trials should be conducted to correlate these findings with clinical significance.