Microdosimetry of kidney cells exposed to ²⁴³ Am and X-ray irradiation

In vitro experiments with rat kidney cells exposed to 243 Am in cell culture medium show a decreasing cell viability with increasing americium concentration. Both the chemical cytotoxicity of americium and the dose caused by ionizing radiation have to be considered as possible causes. To determine the dose rate, a model which was reduced to the dosimetric relevant circumstances was set up. Since the size of the cells is in the micrometer range α -radiation makes the biggest contribution to the dose rate. Using the characteristic behaviour of α -particles the dose rate can be calculated from fluence and stopping power. Biological aspects like uptake of Americium into the cells as well as inaccuracies arising from inhomogeneity and dynamic behaviour in biological systems were taken into account. The dose rate was considered pointwise in the cell center and averaged over the whole cell. Calculations show that dose rates up to the Gy/h range were achieved at the highest americium concentrations of 8⋅10 -4 M. For an experimental comparison of the effect in dependence of the dose reference samples of untreated kidney cells were exposed to analog doses in an X-ray field. Taking relative biological effectiveness into account the cell viability curves depending on the dose show good agreement.