Figure 1 Concept of the therapeutic index Figure 1 | Concept of the therapeutic index. A variety of strategies have shown promise in ameliorating ionizing radiation damage to normal tissues, including protection with radical scavengers, stimulating recovery with cytokines, modifying the p53 response, reducing the negative effects of inflammatory cascades and oxidative stress, and the use of stem-cell therapy. Of note, the slopes of clinical dose–response curves (the relationship between the probability of tumour control and the ionizing radiation dose) indicate that increasing the effective ionizing radiation dose by just 10% (a dose enhancement factor of 1.1) will increase tumour control rates by 5–30%, depending on the tumour site and whether control rates are already low or high121,122. Sharma, R. A. et. al. (2016) Clinical development of new drug–radiotherapy combinations Nat. Rev. Clin. Oncol. doi:10.1038/nrclinonc.2016.79