Ionising irradiation acts primarily via induction of DNA damage, among which double-strand breaks are the most important lesions. These lesions may lead to lethal chromosome aberrations, which are the main reason for cell inactivation. Double-strand breaks can be repaired by several different mechanisms. The regulation of these mechanisms appears be fairly different for normal and tumour cells. Among different cell lines capacity of double-strand break repair varies by only few percents and is known to be determined mostly by genetic factors. Knowledge about double-strand break repair mechanisms and their regulation is important for the optimal application of ionising irradiation in medicine.
