The invention is directed to bodies comprising an amorphous carbon particle on which are supported nanoparticles of an oxide of lanthanide. These bodies find use as a pharmaceutical for use in a surgery or therapy and diagnostic methods. The bodies can be made by a process comprising impregnating a carbon source material by contacting it with a solution of a salt of the lanthanide; drying the impregnated carbon source material; and subjecting the dried impregnated material to pyrolysis under inert conditions.