radiation vs radiotherapy

radiation

noun
  • The transfer of energy via radiation. 

  • The shooting forth of anything from a point or surface, like diverging rays of light. 

  • The process of radiating waves or particles. 

  • A rapid diversification of an ancestral species into many new forms. 

  • Radioactive energy. 

radiotherapy

noun
  • The therapeutic use of ionizing radiation, almost exclusively used for the treatment of malignant disease. 

How often have the words radiation and radiotherapy occurred in a corpus of books? (source: Google Ngram Viewer )