Assessment of the tolerance dose of the hepatic reticulo-endothelial system (RES) after single fraction HDR-irradiation: An in-vivo study employing SSPIO

Abstract

Purpose: To prospectively assess a dose-response relationship for the hepatic reticulo-endothelial system (RES) after small volume single fraction irradiation of liver parenchyma in vivo.Materials and methods: Twenty-five liver tumors were treated by computed tomography (CT)-guided interstitial brachytherapy. Magnetic resonance imaging (MRI) was performed 1 day before and 3 days, 6, 12 and 24 weeks after therapy. MR-sequences included T2-w Turbo Spin Echo (TSE) enhanced by hepatic RES targeted Standard Superparamagnetic Iron Oxide (SSPIO). All MRI data sets were merged with three dimensional (3D) dosimetry data and evaluated by two radiologists. We estimated the threshold dose for either edema or function loss as the D90. A match-pair analysis was performed with another 25 liver tumors, which were treated the same but had MRI follow-up using the hepatocyte specific MRI contrast media Gadobenate dimeglumine (Gd-BOPTA).Results: Three days post brachytherapy the D90 for hepatic RES function loss reached the 18.3 Gray (Gy) isosurface (Standard Deviation (SD) 7.7). At 6 weeks, the respective zone had increased significantly to the 12.9 Gy isosurface (SD 4.4). After 12 and 24 weeks, the dysfunction of liver volume decreased significantly to the 15 Gy and 20.4 Gy isosurface respectively (SD 7.1 and 10.0). Comparison to the hepatocyte function loss indicates a higher minimal threshold dose of the hepatic RES.Conclusion: Hepatic RES demonstrated a high regenerative capacity and a higher minimal threshold dose than hepatocytes. Temporary function loss was found from the 13 Gy isosurface.