Experimental evidence for the use of ultrasound to increase tumor-cell radiosensitivity

One of the most promising applications of ultrasound (US), and in particular of high intensity focused US (HIFU), exploits its capability to increase the sensitivity of cells and tissues to ionizing radiation. We will discuss the different mechanism hypothesized both for normal and cancerous tissues. To give the reader a more general perspective, we describe in some detail the “classical” mechanism underling the radiosensitization, independently of the technical methodology adopted. In this context, we will mention the competitive devices, based on electromagnetic waves, which are also able to increase tissue sensitivity and which are already present in the radiotherapy (RT) world. Then we will concentrate on US as the radiation producing the sensitivity increase. Two main aspects will be treated: thermal and non-thermal effects, in particular in association with microbubbles and nanotechnologies.