- Ionizing radiation (IR) is used to treat more than half of human cancer patients. The therapeutic effect of IR is due to its ability to induce apoptosis. Success of radiation therapy relies not only on apoptosis induction but also on whether surviving cancer cells proliferate and regenerate a tumor. Drosophila melanogaster is a premier genetic model and, relevant to radiation biology of cancer, Drosophila larvae display an amazing capacity to regenerate. IR doses that kill more than half of the cells in larval tissues still allow complete regeneration to produce an adult fly of normal size and pattern. It is by understanding not only the initial effects of IR such as DNA damage and cell death but also longer-term regenerative responses that we may manipulate and improve radiation therapy of cancer. In this regard, Drosophila offers an unparalleled model to study both types of responses.