phototherapy vs radiotherapy

phototherapy and radiotherapy both are nouns.

Word	Noun	Adjective	Verb	Adverb
phototherapy	Yes	No	No	No
radiotherapy	Yes	No	No	No

As nouns, radiotherapy is a hypernym of phototherapy; that is, radiotherapy is a word with a broader meaning than phototherapy:

phototherapy: the use of strong light to treat acne or hyperbilirubinemia of the newborn
radiotherapy: (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance

Other hypernyms of phototherapy include actinotherapy, irradiation, radiation, radiation therapy.

phototherapy (noun)	radiotherapy (noun)
the use of strong light to treat acne or hyperbilirubinemia of the newborn	(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance