About 1-15% cancer patients treated by radiotherapy can showsome early or late significant tissue reactions of different grades(severity), which may limit the application of their treatment andincrease morbidity. These reactions are for instance erythema anddermatitis for breast cancer, proctitis for prostate cancers, fibrosisin oesophageal cancer and lymphomas (Dorr & Hendry, 2001; ICRP,2007). Some rare cases of fatal reactions have been also reportedand are mainly due to mutations of genes essential for DSB repairand signalling like ATM or LIG4 (