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 LI TT in liver tissue, a new thermo-controlled application system was dev eloped. In in vivo experiments in five pigs, ellipsoidal coagulation r egions (3 and 5 cm diameter) were found in the liver within 10 min, wh ich corresponds to a volume of about 20 cm(3). In real time, the incre asing coagulation zone, which appeared as a hyperechogenic halo, could be observed via ultrasound. The power of the laser source during lase r treatment was controlled dynamically via thermosensors. Macroscopica lly and microscopically, the coagulation zones showed well-demarcated borders of the coagulation lesions, and the surrounding tissue appeare d vital. The reparative reaction after irradiation was early fibrosis. For 4 weeks, the surrounding scar capsule, containing fibrocytes, bil iary ductules and collagen fibres, enlarged. As a result, the coagulat ion necrosis became more and more fragmented between collagen fibres, and was largely resorbed. The absence of complications in these pig ex periments suggests that this technique of dynamic laser light applicat ion is safe and useful for therapy of metastases which are not resecta ble.