Indirect lung absorbed dose verification by yttrium-90 PET/CT and complete lung protection by hepatic vein balloon occlusion: proof-of-concept

Abstract

Post-radioembolization lung absorbed dose verification was historically problematic and impractical in clinical practice. We devised an indirect method using yttrium-90 PET/CT. Conceptually, true lung activity is simply the difference between the total prepared activity minus all activity below the diaphragm and residual activity within delivery apparatus. Patient-specific lung mass is measured by CT densitovolumetry. True lung mean absorbed dose is calculated by MIRD macrodosimetry. Proof-of-concept is shown in a hepatocellular carcinoma patient with high lung shunt fraction 26%, where evidence of technically successful hepatic vein balloon occlusion for radioembolization lung protection was required. Indirect lung activity quantification showed the post-radioembolization lung shunt fraction to be reduced to approximately 1% with true lung mean absorbed dose approximately 1Gy, suggesting complete lung protection by hepatic vein balloon occlusion. We discuss possible clinical applications such as lung absorbed dose verification, refining the limits of lung tolerance and the concept of massive activity radioembolization.