Thermo-mechanical damage of biomolecules under ion-beam radiation

The prediction of the relative biological effectiveness of ion beams requires the quantification of all the biomolecular damage processes involved in the interaction of energetic ions with biological media. Traditionally, the damage pathways have been classified as direct or indirect, the former being related to the direct action of the secondary electrons produced along the ion path with DNA molecules, while the latter are referred to the damage produced by the other chemical species generated, mainly free radicals. However, the development over the last years of the multiscale approach to ion beam cancer therapy has revealed the contribution of a new damage mechanism, not present in conventional therapy with photons or electrons: the thermo-mechanical DNA damage arising from the development of shock waves on the nanometer scale around the swift ion path. The present chapter explains the theoretical framework in which this effect is predicted and reviews the work performed over the last years to try to understand the role of this damage pathway in the mechanisms of ion beam cancer therapy.