The present invention relates to the radiotherapy field. In particular, the invention relates to an in vitro method for determining the individual radiosensitivity of a patient. The inventors have in fact identified an individual-radiosensitivity-specific constitutional transcriptomic signature that makes it possible to assess whether a patient is radiosensitive or radiotolerant. The method according to the invention therefore comprises a step of measuring, in a biological sample obtained from a patient, the expression level of at least one gene from the group of 10 genes constituting this signature, namely KLF11, MIR4482, MT-TK, NEK1, PSPHP1, RNU5B-1, RNU6ATAC, RP11-159D12.8, STRN3 and TDG. The present invention makes it possible in particular to adapt the treatments of patients according to their radiosensitivity.