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

Abstract

Background: Many digestive tract tumors spread inside the lumen and are not amenable to curative surgical treatment. An intraluminal method of tumor destruction would be useful for palliative or even curative purposes. High-intensity ultrasound (US) is suitable for such purposes. Our objective was to perform experiments with animal models that would lead to development of a high-intensity US probe for intraductal tumor destruction suitable for insertion through a large-channel endoscope. Methods: The active part of the high-intensity US applicator consisted of a water-cooled piezoceramic plane transducer (3 × 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 flexible shaft. Experiments were conducted in vitro on livers of butchered pigs (10 lesions), in vivo on exteriorized pig livers (15 lesions), and on metastatic Dunning tumors (AT2 subline) implanted subcutaneously in 28 rats (treated n = 16, controls n = 12). Results: In experiments on pig livers, high-intensity US induced highly reproducible cylinders of coagulation necrosis (diameter 20 ± 1 mm, height 8 ± 1 mm) with sharply demarcated and serrated boundaries. The exposure duration to achieve such lesions was 5 minutes. Regions of coagulation necrosis obtained in vivo were similar in size and shape. All 12 control rats died 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 cylinders of coagulation necrosis and is effective against tumors in animals.