radiotherapyEnglishOxford Dictionary of Englishradiotherapy /ˌreɪdiəʊˈθɛrəpi / ▸ noun [mass noun] the treatment of disease, especially cancer, using X-rays or similar forms of radiation. – DERIVATIVES radiotherapeutic /ˌreɪdiəʊˌθɛrəˈpjuːtɪk / adjective radiotherapist /ˌreɪdiəʊˈθɛrəpɪst / noun