[en] Whereas biological studies indicate that double strand breaks in DNA are responsible for cellular death induced by radiations, the physical processes generating such events are not known. For this reason, good parameters to quantify radiation effects are not yet available. In general, no direct relationship is found between the rate of biological damage and the radiation linear energy transfer (LET). This phenomenon may look paradoxal: the lethal efficiency of ions sometimes decreases when the ion LET increases exclamation point Recent interpretations of this effect rely on the characteristics of the energy deposit at the microscopical scale. Whereas energy deposits of 100 eV in 2 nm cubes overlapping DNA are sometimes quoted as critical, here is emphasized a possible dominant role of ion induced K-vacancies in C-atoms of DNA. The existence of a strong correlation between calculated K-vacancy cross sections (ionization + capture) and experimental cell-inactivation cross sections is pointed out and discussed