Tumor treatment with nanosecond pulsed electric fields

Nanosecond pulsed electric fields have demonstrated remarkable potential as tumor therapy. The application of 300-ns pulses with amplitudes of 40-50 kV/cm to melanomas grown in mice caused complete remission of the tumors. It is believed that the primary process that kills the tumor cells is the induction of apoptosis. Electrical models predict that for the application of shorter pulses, higher field strengths are required to trigger this process. By increasing field strength, the field eventually exceeds the dielectric strength of the tissue, especially in the vicinity of the small-diameter needle electrodes used for the exposure. Consequently, discharge phenomena, such as coronas can occur in the tissue. Such non-thermal plasmas, i.e. streamers, could likely assist a tumor therapy by generating reactive oxidative species. We have investigated the regression of tumors that were treated with a coaxial electrode configuration comprised of a 0.4 mm needle electrode in the center of a solid ring electrode of 4 mm radius. A 30-ns/24-kV high voltage pulse of either positive or negative polarity can be applied to the center electrode with respect to the grounded ring-electrode. With positive bias, strong corona discharges can be observed along the needle, while for the opposite polarity, these are either negligible or do not occur. Tumor regression was compared for both conditions and also with results for a 5-needle array of similar dimensions. Preliminary data could not determine any significant immediate advantages of either configuration.