Burst and continuous high frequency irreversible electroporation protocols evaluated in a 3D tumor model

High frequency irreversible electroporation (H-FIRE) is an emerging cancer therapy which uses bursts of alternating polarity pulses to target and destroy the membranes of cells within a predictable volume. Typically, 2 µs pulses are rapidly repeated 24–50 times to create a 48–100 µs long energy burst. Bursts are repeated 100×  at 1 Hz, resulting in an integrated energized time of 0.01 s per treatment. A 3D in vitro tumor model was used to investigate H-FIRE parameters in search of optimal energy timing protocols. Monopolar IRE treatments (100  ×  100 µs positive polarity pulses) resulted in a lethal electric field threshold of 423 V cm⁻¹. Baseline H-FIRE treatments (100  ×  100 µs bursts of 2 µs pulses) resulted in a lethal threshold of 818 V cm⁻¹. Increasing the number of H-FIRE bursts from 100×  to 1000×  reduced the lethal threshold to 535 V cm⁻¹. An alternative diffuse H-FIRE protocol, which delivers 4 µs pulse cycles (one positive and one negative 2 µs pulse) continuously at 100 Hz, resulted in the lowest H-FIRE lethal threshold of 476 V cm⁻¹. Finite element simulations using 5 kV pulses predict an IRE ablation volume of 3.9 cm³ (1.7 cm diameter) and a maximum H-FIRE ablation volume of 5.3 cm³ (2.4 cm diameter) when a clinical electrode and grounding pad configuration is used. Ablations as large as 15.7 cm³ (3.3 cm diameter) are predicted for H-FIRE treatments with 10 kV pulses. These results combine to demonstrate the importance of electrode geometry, pulse timing, and clinical delivery protocols for the creation of large clinically meaningful ablations. (paper)