Relative biological effectiveness (RBE) of alpha radiation in cultured porcine aortic endothelial cells

Purpose: Northern peoples can receive elevated radiation doses (1-10 mSv/y) from transfer of polonium-210 (Po-210) through the lichen-caribou-human food chain. Ingested Po-210 is primarily blood-borne and thus many of its short range alpha particles irradiate the endothelial cells lining the blood vessels. The relative biological effectiveness (RBE) of alpha particles vs. x-rays was examined in porcine aortic endothelial cells as a surrogate for understanding what might happen to human endothelial cells in northern populations consuming traditional foods. Materials and methods: Cultured porcine aortic endothelial cells were exposed to x-ray and Po-210 alpha particle radiation. Alpha irradiation was applied to the cell cultures internally via the culture medium and externally, using thin-bottomed culture dishes. The results given here are based on the external irradiation method, which was found to be more reliable. Dose-response curves were compared for four lethal endpoints (cell viability, live cell fraction, release of lactate dehydrogenase [LDH] and clonogenic survival) to determine the relative biological effectiveness (RBE) of alpha radiation. Results: The alpha RBE for porcine cells varied from 1.6-21, depending on the endpoint: 21.2 +/- 4.5 for cell viability, 12.9 +/- 2.7 for decrease in live cell number, 5.3 +/- 0.4 for LDH release to the medium but only 1.6 +/- 0.1 for clonogenic survival. The low RBE of 1.6 was due to x-ray hypersensitivity of endothelial cells at low doses.