Background: In clinical practice the dose of Y90 Sir-Spheres is calculated using a pre injection of Tc99m MAA. There is however a potential difference due to the different properties of Tc99m MAA and Y90 Sir-Spheres. We assessed the concordance of lung shunting of Y90 Sir-Spheres estimated using Y90 Bremsstrahlung imaging, compared to shunting assessed using Tc99m MAA.

Methods: 15 Patients were evaluated using 150-200 MBq of Tc99m MAA injected into the hepatic artery under angiographic guidance. Wholebody images were acquired using a LEAP collimator (window of 140 kEv+/-10%). The patients were subsequently treated with Y90 Sir-Spheres. After microspheres injection, whole body brehmsstrahlung images were acquired using a medium energy collimator (window settings of 75 kEv +/- 20%). Tc99m MAA images were paired with their corresponding bremsstrahlung image and lung shunting in the stuides calculated simultaneously. Each paired dataset was analyzed by 5 operators.

Results: The mean lung shunting for Tc99m MAA acquisition was 3.32% (SD 2.03) which was significantly lower than the lung shunting using the Y90 acquisitions: mean 16.19% (SD of 6.43). The Pearson coefficient was r = 0.62 (p<0.02).

Conclusion: The lung shunting calculated by Y90 Sir-Spheres bremsstrahlung imaging is higher than that calculated by Tc99m MAA imaging. The relationship is not sufficiently strong to use bremsstahlung imaging to retrospectively quantify the lung-to-liver shunting as indicated using Tc99 MAA. Further studies are underway to assess the reliability of Tc99m MAA lung uptake calculations in determining the dose of Y90 Sir-Spheres.