Radiofrequency ablation of renal tumors improved by preoperative ex-vivo computer simulation model

Radiofrequency ablation (RFA) of small renal tumors has emerged as an option for patients with contraindications to surgery. The technique usually is limited to dorsolateral tumors because of the unknown pattern of heat distribution. The aim of this in-vitro experiment was to develop a planning computer simulation model of the heat distribution in order to calculate needle placement correctly.

Our measurement system enables capture of the temperature pattern of a linear arrangement of thermocouples in a porcine cadaver kidney. A high-frequency sinusoidal electric current (460 kHz) was introduced via a unipolar umbrella-shaped needle electrode. The results of the RFA thermocoagulation were compared with the computer model using the finite element method.

Comparison between ex-vivo simulation and in-vivo measurement of destruction in three porcine cadaver kidneys showed excellent agreement. The discoloring of the necrotic region represented a temperature of 42 degrees C, where the tissue begins to denaturate. The 42 degrees C isodose temperature could be simulated precisely starting 6 mm from the center of the needle electrode. Using several MATLAB programs, simulation models were created to predict the space and time correlation of the necrotic regions.

This experimental model allows successful planning of the expected necrotic region using RFA in a cadaver kidney. Future planning can be improved by using a perfused in-vivo kidney model, thus allowing much more precise computer simulation before applying RFA to kidney tumors at critical locations.