[Dynamic interstitial laser application for therapy of secondary liver tumors. An animal experiment study]

Laser-induced interstitial thermotherapy (LITT) is a promising method of treating different types of tumors. To increase the effectiveness of LITT, a new thermo-controlled application system for minimal invasive intervention was designed. This laser system consists of a laser applicator 3 mm in diameter, insertion equipment and an Nd:YAG laser source. The power of the laser source is controlled dynamically by thermosensors in a water-cooling system of the laser applicator. In in vivo experiments in five pigs, within 10 min we found homogeneous coagulation regions in the liver that were of 3 cm and 5 cm in diameter. Via ultrasound we observed in real time the increasing coagulation zone that appeared as a hyperechogenic halo. However, due to perifocal edema, the real coagulation area was smaller than detected by ultrasound. Macroscopically and microscopically, the coagulation zones showed well-demarcated borders of the coagulation lesions, and the surrounding tissue appeared vital. The reparative reaction after irradiation was early fibrosis. In the course of 4 weeks, the surrounding scar capsule, containing fibrocytes, biliary ductules and collagen fibers enlarged. As a result, the coagulation necrosis became more and more fragmented between collagen fibers and was largely resorbed. The absence of complications in our animal experiments suggest that the technique of thermo-controlled laser light application is safe and useful in therapy for metastases that are not resectable.