I have some info on that:
- The danger of ionising radiation became apparent after the discovery of X-rays in 1895.
- Most of the first generation of radiation therapists in the early 1900s died of cancer.
- The effects of UV radiation have also been known for some time. In 1905, cases of skin cancer were recorded on the necks of grape pickers who were exposed to the sun for long periods.
- Further evidence for the mutagenic nature of ionising radiation came with the development of nuclear weapons (atomic bomb on Hiroshima) and nuclear reactors (Chernobyl disaster). In both these areas, there has been an increase in the frequency of cancers, particularly leukemia.
Hope that helped.