Interstitial laser-induced thermotherapy: influence of carbonization on lesion size.
OBJECTIVE
The size of laser-induced coagulated lesions produced in porcine muscle in vitro using a cylindrical diffusing fiber tip and a conductive heat source, made by covering the diffuser with a hollow steel needle, were compared to investigate the influence of charring.


METHODS
Light from a Nd:YAG laser was utilized for thermotherapy. A theoretical model for calculating tissue temperature was used to predict the experimental results and to simulate in vivo treatments.


RESULTS
The metal-covered tip produced carbonization 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 cm3 (range 12.4-14.1 cm3, n = 4) and 12.2 cm3 (range 11.5-13.4 cm3, n = 4), respectively. Mathematical simulations showed that in unperfused tissue, a diffusing laser heat source produces smaller lesions than does a conductive heat source at the same power, the difference in coagulated volume becoming smaller with increased treatment time and increased power.


CONCLUSIONS
Using cylindrical diffusers, interstitial laser-induced thermotherapy without carbonization at the fiber tip can be as efficient as treatment with carbonization.
Sturesson
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Department of Physics, Lund Institute of Technology, Sweden. Christian.Sturesson@fysik.lth.se
D000818:Animals; D001831:Body Temperature; D005110:Extracellular Space / Q000528:radiation effects*; D006358:Hot Temperature; D006979:Hyperthermia, Induced / Q000379:methods*; D007834:Lasers; D008099:Liver / Q000166:cytology / Q000502:physiology / Q000528:radiation effects; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology / Q000528:radiation effects; D013552:Swine; D014422:Turkeys