Interstitial Laser Thermotherapy of Liver Tumours. Methodology and Application

Abstract: Interstitial laser thermotherapy (ILT) is a method well suited for selective local destruction of malignant tumours. In the present work, a laser thermotherapy system based on feedback temperature control of energy delivery (through computerised feedback system) was developed. Temperature control was excellent in experiments without carbonization and with preserved light penetration, whereas temperature oscillations were large in experiments with carbonization and impaired light penetration. Using bare fibre, carbonization was seen in almost all experiments in vitro, regardless of output power (1-4 W) but only occasionally in vivo using 2 W. Treatment with a sapphire probe, representing a diffuser tip, gave carbonization at higher output powers (> 3 W in vitro, > 4 W in vivo). The bare fibre gave a steeper temperature gradient than the sapphire probe. In normal pig liver the volume of thermal damage was increased five times by occluding the blood flow to the liver during treatment. It was not possible to predict the size of thermal damage in normal pig livers using ultrasonography. The effect of different temperatures and different treatment times was studied in rats with transplanted liver tumours. It appeared that total tumour necrosis was obtained with a temperature of 54-61°C at the tumour margin and a treatment time of 30 min. In a subsequent study, ILT (46°C for 30 min) was based on these findings and compared with resection of the tumour-bearing liver lobe. There was no difference in local tumour control but the incidence and extent of intraabdominal spread was lower after ILT than after resection. ILT was used in patients with irresectable tumours, and problems concerned with monitoring of thermal damage and limited volume effect were identified.