Electrode Tip Wear Increases Needle Deflection and Procedural Complexity in Electrochemotherapy

Electrochemotherapy (ECT) is a widely accepted treatment modality for skin cancers that are not amenable to first-line therapies. It is extensively used in both human and veterinary medicine. Various electrode designs exist, with needle tips differing by manufacturer and application. In human medicine, electrodes commonly feature conical tips, while veterinary electrodes typically have sharper, beveled tips to better penetrate the tougher skin of animals. A recurrent issue among ECT practitioners-both physicians and veterinarians-is the progressive loss of needle sharpness during treatment. This degradation increases tissue trauma, potentially delaying recovery, particularly when treating healthy surgical margins. In addition, blunted needles are prone to deflection upon insertion, which alters the inter-needle spacing. This, in turn, can compromise the uniformity of electric field distribution and leave regions of the target tissue insufficiently permeabilized.

Three needle tip geometries-conical, beveled, and triangular-were evaluated. All needles had a diameter of 7 mm. COMSOL Multiphysics® simulations were performed to assess electric field distribution for each tip type. Insertion force and the number of insertions until noticeable loss of sharpness were evaluated using an ex vivo model. In addition, the use of a guiding mask integrated into the electrode design was tested to minimize needle deflection during insertion.

COMSOL simulations showed that near the needle tip, the electric field intensity in the space between needles remained below the minimum threshold for effective tissue permeabilization, with similar patterns across all tip types. Conical tips required the highest insertion force, followed by beveled and then triangular tips. Sharpness degradation occurred most rapidly in conical needles, with significant dulling after approximately 50 insertions. Beveled tips retained functional sharpness for about 150 insertions, while triangular tips maintained it for up to 200 insertions. Triangular needles demonstrated superior insertion efficiency and durability. The inclusion of a guiding mask substantially reduced needle deflection, improving parallel alignment and maintaining electric field uniformity.