Limitations of the radiosensitivity index as a direct prognostic marker

Radiotherapy is a vital therapeutic intervention, and the prospect of personalising and optimising treatment on the basis of a patient's genomic profile and intrinsic radiosensitivity holds great allure. An influential work by Eschrich and colleagues1 (2009) introduced the radiosensitivity index concept, presenting evidence that the differential expression of ten genes was predictive of the fraction of cells of a particular type surviving exposure to a single 2-Gy dose of conventional photon x-ray radiation (a fraction known as SF2).