Claesson, A. K., Stenerlöw, B., Jacobsson, L. and Elmroth, K. Relative Biological Effectiveness of the α-Particle Emitter ²¹¹At for Double-Strand Break Induction in Human Fibroblasts. Radiat. Res. 167, 312–318 (2007).

The purpose of this study was to quantify and to determine the distribution of DNA double-strand breaks (DSBs) in human cells irradiated in vitro and to evaluate the relative biological effectiveness (RBE) of the α-particle emitter ²¹¹At for DSB induction. The influence of the irradiation temperature on the induction of DSBs was also investigated. Human fibroblasts were irradiated as intact cells with α particles from ²¹¹At, ⁶⁰Co γ rays and X rays. The numbers and distributions of DSBs were determined by pulsed-field gel electrophoresis with fragment analysis for separation of DNA fragments in sizes 10 kbp–5.7 Mbp. A non-random distribution was found for DSB induction after irradiation with α particles from ²¹¹At, while irradiation with low-LET radiation led to more random distributions. The RBEs for DSB induction were 2.1 and 3.1 for ⁶⁰Co γ rays and X rays as the reference radiation, respectively. In the experiments studying temperature effects, nuclear monolayers were irradiated with ²¹¹At α particles or ⁶⁰Co γ rays at 2°C or 37°C and intact cells were irradiated with ²¹¹At α particles at the same temperatures. The dose-modifying factor (DMF_temp) for irradiation of nuclear monolayers at 37°C compared with 2°C was 1.7 for ²¹¹At α particles and 1.6 for ⁶⁰Co γ rays. No temperature effect was observed for intact cells irradiated with ²¹¹At. In conclusion, irradiation with α particles from ²¹¹At induced two to three times more DSB than γ rays and X rays.