Dosimetric investigations of dynamic effects during Immunostimulating Interstitial Laser Thermotherapy

Abstract: A simulation model of immunostimulating Interstitial Laser Thermotherapy (imILT) has been developed to investigate the effect that biological variations in tissues have on the treatment outcome. The biological variations include optical and thermal properties. The model based on the results of these investigations was further developed to investigate the possibility of predicting an imILT treatment outcome on ex vivo bovine cardiac muscle tissue, and experiments were performed to validate the simulations. An imILT treatment is based on laser induced tissue ablation due to heat generation via light absorption. The optical properties, i.e. the absorption and the reduced scattering coefficient, affect the treatment outcome in a similar way. An increase in these coefficients yields a faster temperature rise closer to the light source. Furthermore it was seen that it is important to take into consideration a change in optical properties related to thermal coagulation of tissue since the optical properties of coagulated tissue are significantly different from non-coagulated tissue of the same type due to the increased scattering. The effect of varying the thermal properties on the treatment outcome was found to be governed by heat conductivity. Changes in the model were thus made to account for the effects due to tissue coagulation and the heat conductivity by implementing a dynamic relationship between temperature and the optical and thermal properties. The simulated results were found to be in good qualitative agreement with the experiments.