X-ray therapy vs radiotherapy

X-ray therapy and radiotherapy both are nouns.

Word	Noun	Adjective	Verb	Adverb
X-ray therapy	Yes	No	No	No
radiotherapy	Yes	No	No	No

As nouns, radiotherapy is a hypernym of X-ray therapy; that is, radiotherapy is a word with a broader meaning than X-ray therapy:

X-ray therapy: the therapeutic use of X rays
radiotherapy: (medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance

Other hypernyms of X-ray therapy include actinotherapy, irradiation, radiation, radiation therapy.

X-ray therapy (noun)	radiotherapy (noun)
the therapeutic use of X rays	(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance