radiotherapy vs radiation therapy

radiotherapy and radiation therapy both are nouns.

Word	Noun	Adjective	Verb	Adverb
radiotherapy	Yes	No	No	No
radiation therapy	Yes	No	No	No

As nouns, radiotherapy and radiation therapy are synonyms defined as:

radiotherapy and radiation therapy: (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance

Other synonyms of radiotherapy include actinotherapy, irradiation, radiation.

radiotherapy (noun)	radiation therapy (noun)
(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance	(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance