Supposing radiation causes cancer, will that cancer be treated with more radiation?

Maybe: Sounds paradoxical, doesn't it? But it works. Radiation damages the genome and the mutations may eventually give rise to a cancer. Big doses simply cause cells of all kinds to die off, many cancers being vulnerable. The radiation-induced cancers are most often sarcomas or leukemias; a sarcoma may be palliated by a big dose of radiation (it's actually more toxic to fully-developed cancer cell.