A high-intensity US probe designed for intraductal tumor destruction: experimental results

Background: Many digestive tract tumors spread inside the lumen and are not amenable to curative surgical treatment. An intraluminal method of tumor d estruction would be useful for palliative or even curative purposes. High-i ntensity ultrasound (US) is suitable for such purposes. Our objective was t o perform experiments with animal models that would lead to development of a high-intensity US probe for intraductal tumor destruction suitable for in sertion through a large-channel endoscope. Methods: The active part of the high-intensity US applicator consisted of a water-cooled piezoceramic plane transducer (3 x 10 mm) operating at 5 MHz for deep or 10 MHz for shallow tissue penetration. A cylinder of tissue was destroyed by means of rotating the transducer on its axis through a flexib le shaft, Experiments were conducted in vitro on livers of butchered pigs ( 10 lesions), in vivo on exteriorized pig livers (15 lesions), and on metast atic Dunning tumors (AT(2) subline) implanted subcutaneously in 28 rats (tr eated n = 16, controls n = 12). Results: In experiments on pig livers, high-intensity US induced highly rep roducible cylinders of coagulation necrosis (diameter 20 +/- 1 mm, height 8 +/- 1 mm) with sharply demarcated and serrated boundaries. The exposure du ration to achieve such lesions was 5 minutes. Regions of coagulation necros is obtained in vivo were similar in size and shape. AII 12 control rats die d or were killed because of diffuse cancer by day 15 after implantation; 64 % of the treated rats were tumor free 30 days after treatment, and 36% had local recurrences. Conclusion: This high-intensity US probe induces highly reproducible cylind ers of coagulation necrosis and is effective against tumors in animals.