Proving Feasibility of Titanium Radiation Seeds for Prostate Cancer Brachytherapy Used Simultaneously as Heating Mediators for Magnetic Hyperthermia

The induction heating ability of Ti needles (φ 0.8 mm × 4.5 mm) was measured by applying an alternating magnetic field of 800∼990 kHz up to 50 Oe-rms. The needles were cold dummies of small radiation seeds (titanium capsule: φ 0.8 mm × φ 0.64 mm × 4.5 mm) used in prostate cancer brachytherapy; the needles and seeds have roughly equal potential to heat up because of eddy current losses. Eddy current losses are concentrated at the outer circumference of heating generators. Under a 990 kHz magnetic field of 40 Oe-rms, 1 ml of starch paste inserted with a Ti needle (either perpendicular or parallel to the magnetic field) was heated above 42.5°C, a threshold temperature required to kill cancer cells. Furthermore, 40 Ti needles were inserted into an artificial prostate (φ 36 mm × 20 mm) made of polyacrylamide gel. The artificial prostate was then immersed in 36°C water, and a 990 kHz-40 Oe-rms magnetic field was applied for 20 minutes, which increased the temperature of the inner part of the artificial prostate to above 42.5°C. However, the peripheral part was kept at a lower temperature. Therefore, when the radiation seeds are jointly used as heating mediators for hyperthermia, thermal damage to organs surrounding the prostate may be suppressed. Prostate cancer tissue was implanted on a mouse and grown to 3 ml in volume. Three Ti needles were then inserted into the tumor. After exposure to a 990-kHz-50-Oe-rms magnetic field for 20 minutes, the model tumor was successfully heated above 44.5°C, while the surface temperature of the mouse's body was kept below 38°C. All of these results indicate a promising combination of prostate brachytherapy and magnetic hyperthermia, using the Ti radiation seeds as heating mediators.