Development of a radiofrequency based thermal therapy technique in an in vivo porcine model for the treatment of small renal masses

Purpose: Incidentally detected small renal tumors appear to grow slowly and be localized to the kidney, Minimally invasive therapies are being investi gated as alternatives to standard surgical techniques. Radiofrequency ablat ion has been reported for the treatment, of small renal cell carcinomas. We developed a radiofrequency technique and established its efficacy and safe ty in a large animal model. Materials and Methods: A total of 22 lesions were created in normal kidneys of 7 pigs. Radiofrequency energy was administered during open exposure of the kidneys or percutaneously under ultrasound guidance. Lesion development was monitored with gray-scale and power Doppler ultrasound. To avoid heati ng surrounding tissues new hydro-dissection and gas-dissection techniques w ere developed. Lesion sizes and characteristics were assessed by ultrasound and pathological examination. Results: No complications were observed due to probe insertion and removal. Perirenal structures were thermally damaged before the development and app lication of the dissection techniques. Lesion size was accurately predicted by gray-scale ultrasound on day 7. Loss of perfusion in the ablated volume was confirmed by power Doppler ultrasound. Lesions were wedge-shaped, pres umably due to the effects of heating on segmental blood flow distribution. Pathological examination revealed changes consistent with thermal injury an d ischemic type infarction. Conclusions: Radiofrequency thermal therapy is an effective and efficient m ethod for ablating normal renal tissue in the pig. It may be applied percut aneously under ultrasound guidance with minimal complications provided that vital adjacent structures are protected from thermal damage. Further studi es are required in humans before adopting this technique as definitive trea tment for small renal cell carcinoma.