Abstract: Implantable seeds, comprising rod-shaped ferromagnetic elements with end caps that contain radioactive pellets, designed for,delivering both thermal radiation and ionizing radiation for treatment of tumorous tissue are described. The implantable seeds can also contain additional radioactive pellets positioned in hollow tubular sleeves that connect a series of ferromagnetic elements. The ferromagnetic material may be a palladium-cobalt (Pd—Co) alloy with a Curie temperature between about 40 C. and 100 C., and the end caps and tubular sleeves may be made of titanium. Alternatively, the ferromagentic elements may comprise rods with longitudinal channels in their outer surfaces, into which radioactive sources are positioned. This assembly is held together by an outer tubular sleeve or coating. The radioactive pellets comprise either palladium-103 or iodine-125. Methods of making the seeds and of delivering treatment to a patient are also described.