Model of electric field and the help system of BK92A instrument for ECT
Pang Hongbing, Xin Yuling
(Beijing University ofAeronautics and Astronautics,100083)

During the treatment of ECT(electrochemical therapy), dynamic observation on the specimens taken from positive electrode treating area and negative electrode area. Was conducted at different time, distance and electric quantity, PH value and temperature were measured regularly. After treatment, specimens was made into paraffin big sections to observe necrotic area, and dealt it with computer. The result showed that positive electrode appears coagulated necrosis and around negative electrode appears Iiquiefied necrosis, the two electrodes(only two electrodes) has the same kill-range. The maximal irreversiboe kill-range of each electrode is about 3cm.

We had developed one mode! System of electric field with Computer to show the effects of the electric field distribution. An important conclusion can be drawn: the main body of electric field looked like a cylinder, which axis is the electrode, and diameter is about 3cm. Beyond the cylinder, the electric field is very weak. It means that the current density at every point around the electrode inversely proportional to the distance between the point and electrode as well as the dielectric constant of tissue at the point. The cancer cell was damaged by ion movement, i.e. the current, in the electric field.

More experiments had been done for verifying the conclusion. And the following points were obtained:

1.  The damaged areas of the anode and cathode are about the same when the number of anodes equals the number of cathodes and the distribution of each pair of anode and cathode is strictly symmetric, especialy when only two electrodes are applied.

2.  The damage area is proportional to the electric quantity, when the electric quantity is less than 100 coulomb per cm. The size of damaging area would not increase with the increase of electric quantity, if the quantity is greater than 100C/cm. So, if the tumor is very big, more electrodes should be used in stead of just increasing the electric quantity.

Based on the mode! of electric field and experiment data, a help System of ECT has been developed and equipped into BK92A Advanced Instrument for ECT. If the size of tumor is input into the system, suitable parameters of electrode and necessary electric quantity can be given automatically. lt is helpful to clinical use on ECT.