Evaluation of a fuzzy logic controller for laser thermal therapy

Laser thermal therapy (LTT) is a minimally invasive surgical technique used to destroy solid tumors while minimizing damage to adjacent normal tissues. Optical energy, delivered through fibers implanted into the target volume, raises tissue temperatures above 60degreesC resulting in coagulative necrosis (thermal damage). Thermal damage volumes, however, can be irregular and unpredictable, resulting from dynamic changes in the tissue properties during treatment. A closed-loop feedback fuzzy logic controller for LTT was developed with the tissue treated as a "black-box" system. Preliminary testing was conducted for simulated LTT with a single spherically emitting source fiber at the center of 5 turn and 10 mm diameter target tissues. Dynamic changes in blood perfusion and tissue optical properties due to heating were incorporated into the LTT simulator. Input laser power was modulated to control the temperature field in an attempt to reach target temperatures at the source (90degreesC to avoid tissue charring) and at the target boundary (55degreesC). In all simulations, thermal damage based on Arrhenius formulation (Omega = 1) was reached at the target boundary. The controller also responded efficiently to unexpected, rapid temperature changes.