A radiation therapy system includes a radiation source capable of generating a beam of radiation a magnetic resonance imaging (MRI) apparatus comprising at least one radiofrequency detector coil and an electrically grounded dielectric material between the radiation source and the radiofrequency detector coil for shielding the at least one radiofrequency detector coil from the beam of radiation. Also disclosed is a radiofrequency detector coil for a magnetic resonance imaging (MRI) apparatus sheathed at least in part by a dielectric material that is adapted to be electrically grounded.
