INTERSTITIAL LASER-INDUCED THERMOTHERAPY - INFLUENCE OF CARBONIZATIONON LESION SIZE

Background and Objective: The size of laser-induced coagulated lesions produced in porcine muscle in vitro using a cylindrical diffusing fib er tip and a conductive heat source, made by covering the diffuser wit h a hollow steel needle, were compared to investigate the influence of charring. Materials and methods: Light from a Nd: YAG laser was utili zed for thermotherapy. A theoretical model for calculating tissue temp erature was used to predict the experimental results and to simulate i n vivo treatments. Results: The metal-covered tip produced carbonizati on and tissue vaporization that was not found with the diffuser. After 20 min of irradiation at a laser power of 7 W, the coagulated volumes with and without carbonization were found to be 13.1 cm(3) (range 12. 4-14.1 cm(3), n = 4) and 12.2 cm(3) (range 11.5-13.4 cm(3), n = 4), re spectively. Mathematical simulations showed that in unperfused tissue, a diffusing laser heat source produces smaller lesions than does a co nductive heat source at the same power, the difference in coagulated v olume becoming smaller with increased treatment time and increased pow er. Conclusion: Using cylindrical diffusers, interstitial laser-induce d thermotherapy without carbonization at the fiber tip can be as effic ient as treatment with carbonization. (C) 1998 Wiley-Liss, Inc.