Laser coagulation zones induced with the Nd-YAG laser in the liver

Laser-induced interstitial thermotherapy (LITT) has become a method to treat different types of tumours. To increase the effectiveness of LITT in liver tissue, a new thermo-controlled application system was developed. In in vivo experiments in five pigs, ellipsoidal coagulation regions (3 and 5 cm diameter) were found in the liver within 10 min, which corresponds to a volume of about 20 cm(3). In real time, the increasing coagulation zone, which appeared as a hyperechogenic halo, could be observed via ultrasound. The power of the laser source during laser treatment was controlled dynamically via thermosensors. 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. For 4 weeks, the surrounding scar capsule, containing fibrocytes, biliary ductules and collagen fibres, enlarged. As a result, the coagulation necrosis became more and more fragmented between collagen fibres, and was largely resorbed. The absence of complications in these pig experiments suggests that this technique of dynamic laser light application is safe and useful for therapy of metastases which are not resectable.