We propose a multiscale approach to understand the physics related to ion-beam cancer therapy. It allows the calculation of the probability of DNA damage as a result of irradiation of tissues with energetic ions, up to $430\mathrm{MeV}∕\mathrm{u}$. This approach covers different scales, starting from the large scale, defined by the ion stopping, followed by a smaller scale, defined by secondary electrons and radicals, and ending with the shortest scale, defined by interactions of secondaries with the DNA. We present calculations of the probabilities of single and double strand breaks of DNA, suggest a way to further expand such calculations, and also make some estimates for glial cells exposed to radiation.

Radiation damage following the ionising radiation of tissue has different scenarios and mechanisms depending on the projectiles or radiation modality. We investigate the radiation damage effects due to shock waves produced by ions. We analyse the strength of the shock wave capable of directly producing DNA strand breaks and, depending on the ion's linear energy transfer, estimate the radius from the ion's path, within which DNA damage by the shock wave mechanism is dominant. At much smaller values of linear energy transfer, the shock waves turn out to be instrumental in propagating reactive species formed close to the ion's path to large distances, successfully competing with diffusion.

Ion-beam cancer therapy, an alternative to a common radiation therapy with X-rays, has been used clinically around the world since 1990s; the number of proton therapy centers as well as facilities using heavier ions such as α-particles and carbon ions continues to grow. A number of different methods were used by various scientific communities in order to quantitatively predict therapeutic effects of application of ion beams. A Multiscale approach (MSA) reviewed in this paper is one of these methods. Its name reflects the fact that the scenario of radiation damage following the incidence of an ion beam on tissue includes large ranges of scales in time, space, and energy. This review demonstrates the motivation and scientific justification of the MSA to the physics of ion-beam therapy and its implementation to a variety of different limits and physical conditions. A number of examples of calculations at high and low values of linear energy transfer (LET), large and small ion fluences, for a single value of LET and a combination of LETs in a spread-out Bragg peak are presented. The MSA has integrated the science involved in ion-beam therapy; in the process of the development of MSA, a new physical effect of ion-induced shock waves has been predicted. Its effect on the scenario of radiation damage is discussed in detail. Multiscale approach’s predictive capabilities are based on the fundamental scientific knowledge. Their strength is in relation to actual physical, chemical, and biological processes that take place following the ions incidence on tissue. This makes the approach flexible and versatile to include various conditions, such as the degree of aeration or the presence of sensitizing nanoparticles, related to particular cases. The ideas for how the MSA can contribute to an improved optimization of therapy planning are summarized in the review.