Calculation of the electrical parameters in electrochemotherapy of solid tumours in mice D. S Ï emrov*, D. MiklavcÏicÏ University of Ljubljana, Faculty of Electrical Engineering, Trz ÏasÏka 25, SI-1000 Ljubljana, Slovenia Received 8 December 1997 Abstract Electrochemotherapy is a novel approach in chemotherapeutic drug delivery into tumours. Short intense direct current electric pulses are applied to tumour tissue causing electropermeabilisation thus enabling entrance of chemotherapeutic drugs into cells which otherwise do not easily penetrate. A three dimensional anatomically based ®nite element model of the mouse with injected subcutaneous solid tumour was built. The main goal of the study was to evaluate the in¯uence of the electrode orientation on the distribution of electric ®eld in the tumour and surrounding tissue during electrochemotherapy. Two electrode con®gurations, previously examined in experimental study, were modelled. Electric ®eld distributions were calculated for each con®guration. The main conclusion of our study is that changing electrode orientation strongly in¯uences the distribution of the electric ®eld inside the tumour in the electrochemotherapy of solid tumours in mice, which is in good agreement with the results of the experimental study. The ecacy of the electrochemotherapy depends on the magnitude of the electric ®eld intensity inside tumour tissue. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Electrochemotherapy; Electroporation; Murine tumour models; Electrode con®guration; Numerical modelling; Finite element method 1. Introduction Electric conductivity of the plasma membrane in normal physiological conditions is much lower than the conductivity of cytoplasm and extracellular medium. When a cell is exposed to an external electric ®eld, the anode-facing side becomes hyper-polarized and the cathode-facing side becomes depolarized depending on the size and the shape of the cell [1]. If the externally induced transmembrane potential is high enough, then reversible permeabilization of plasma Computers in Biology and Medicine 28 (1998) 439±448 0010-4825/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved. PII: S0010-4825(98)00017-1 PERGAMON * Corresponding author. Fax: +386-61-126-46-58; E-mail: dejan@svarun.fe.uni-lj.si.