IPA: //ˌreɪ.di.oʊˈθɛr.ə.pɪst//
KK: /ˈreɪdiəʊˌθɛrəpɪst/
A healthcare professional who uses radiation to treat patients, often for cancer.
The radiotherapist explained the treatment plan to the patient.
Radiotherapist → It is formed from "radio-" (from Latin "radius", meaning ray) and "therapist" (from Greek "therapeutes", meaning one who treats). The word refers to a person who treats diseases using rays, typically in the context of radiation therapy.
Think of 'rays' ('radio-') being used by a 'treating person' ('therapist') to help heal someone.