radium therapy vs radiotherapy

radium therapy and radiotherapy both are nouns.

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

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

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

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

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