Focussed extracorporeal pyrotherapy: experimental results

A new device made of piezoelectric ceramic placed in a semispherical dish and focussed at 320 mm was developed in order to generate heat and cavitation responsible for coagulative necrosis of deep tissues. The target to be treated is located with a central ultrasound probe of 3.5 MHz. In vitro studies with polyurethane phantoms showed that the ultrasound melted a surface of 2 x 12 mm within 1 s. The temperature recorded at the focus was 270 degrees C. In tissue samples (prostate cancer and benign prostate hyperplasia), the temperature rose to 85 degrees C in vitro and a hyperechoic zone appeared at the focus during shots. In vivo 8-mm plastic spheres, introduced surgically into the bladder of pigs, were melted by repeat shots without burning of crossed tissues. These studies were performed in the kidney and the liver. Autopsy performed on day 0 showed congestion, autopsy performed between day 6 and day 11 showed necrosis, whereas at 3 months the focussed area was fibrosed. This technique, which we called 'focussed extracorporeal pyrotherapy', combines phenomena of cavitation and high heat at the focus. Prostate tumors, bladder tumors, kidney tumors and liver metastases are potential indications for pyrotherapy.