Radiotherapy apparatus comprising: a vacuum chamber (20) in which is provided an electron source (22) capable of emitting an electron beam; a radiation-generating target anode (27) capable of generating X-rays in response to the incidence of the electron beam thereon; and a rod-shaped conduit (24) for guiding the electron beam to the anode which is located at a distal end thereof, characterised in that the electron source comprises an indirectly heated electron-emissive cathode.
