Development of Ni-4 wt.% Si thermoseeds for hyperthermia cancer treatment

Ferromagnetic alloys, used in the form of "thermoseeds" for surgical implantation, have been developed and used to induce localized hyperthermia in cancerous growths. Alloys of nickel with approx. 4 wt.% Si were chosen for this study because they have Curie temperatures in the desired range of 45-60 degrees C. The thermoseeds were prepared by using either a special casting technique or casting and swaging followed by homogenization. The effects of these different processing schedules on the magnetic behavior of these alloys are discussed. In particular, the importance of minimizing oxidation during melting and heat treating, and the effects of homogenizing the thermoseeds on the relative permeability at temperatures near the Curie temperature are pointed out. The best processing schedule is casting small ingots while avoiding oxidation, followed by swaging, drawing, and homogenization. Actual induction heating experiments and the results from magnetization tests indicate that Ni-4 wt.% Si alloys prepared in this manner can be used as thermoseeds with predictable Curie temperatures. These thermoseeds can be used to obtain nearly uniform and constant temperatures in tumors with variable blood flows.