Dynamic modeling of interstitial laser photocoagulation: implications for lesion formation in liver in vivo

Interstitial Laser Photocoagulation (ILP) is a minimally invasive cancer treatment technique, whereby optical energy from implanted optical fibers is used to therapeutically heat small, solid tumors. In this work, the potential of ILP without tissue charring is investigated.

Optical diffusion and bio-heat transfer equations were used to develop dynamic models of interstitial laser heating in liver in vivo. Modifications in the optical properties due to tissue coagulation (T > or = 60 degrees C) were incorporated into the physical description. In addition, the effect of three different blood perfusion patterns on temperature distributions was explored. Model-predicted temperatures were used as an index for thermal damage based on an accumulated temperature injury (Arrhenius) model. Thermal damage dimensions were determined with tissue temperatures constrained to remain below 100 degrees C, so as to minimize the potential for tissue charring and smoke production.

The model predicts that increases in scattering due to coagulation and choice of perfusion pattern affect substantially thermal damage dimensions. The results indicate that, for single fiber ILP at 2.55 W for 600 s, the maximum achievable thermal damage diameter in liver, without charring, is 9.6 mm. In addition, ILP performed with high-low power ramping may have an advantage over constant power treatments, in that, larger volumes of thermal damage can be realized earlier in an irradiation.

For ILP performed with a single spherical emitting fiber, optimal irradiation parameters exist such that thermal lesions in liver up to approximately 10 mm in diameter can be induced while the maximum tissue temperature remains below 100 degrees C, avoiding tissue charring.