History of radiation therapy
The history of radiation therapy or radiotherapy can be traced back to experiments made soon after the discovery of X-rays (1895), when it was shown that exposure to radiation produced cutaneous burns. Influenced by electrotherapy and escharotics—the medical application of caustic substances—doctors began using radiation to treat growths and lesions produced by diseases such as lupus, basal cell carcinoma, and epithelioma.
Source: Wikipedia — History of radiation therapy (CC BY-SA 4.0)