Radiotherapeutic apparatus comprising: magnetic coils 16 disposed around a patient support 10 for creating a magnetic field, where the coils 16 have a longitudinal axis I and the magnetic field is created parallel to the longitudinal axis I； a radiation source 6 producing a beam of radiation directed toward the patient support 10 and which is mounted on a rotatable support 28 to rotate radiation source 6 around patient support 10； and a slip ring located around patient support 10 for conveying electrical power to radiation source 6 and where the slip ring is broken into a plurality of arc segments or contact points 88；and a plurality of power cables 70, each running from a respective arc segment 88 to a power source, with each power cable 70 comprising a section parallel to the longitudinal axis I and extending from its respective arc segment 88 to a point beyond the longitudinal extent of the coils 16. Rotatable support 28 may comprise at least one brush contact arranged to contact the slip ring to convey electrical power to the radiation source 6. Radiation source 6 may be a linear accelerator. The apparatus may further comprise a magnetic field detecting imaging means.
