A Simplified Model of Laser Hyperthermia of Superficial Tumors Including Variation of Human Tissue Optical Properties With Thermal Damage

Laser induced hyperthermia is a promising tool in a fight with human cancer especially with superficial deceases such as carcinoma or melanoma. A correct choice of the thermal treatment parameters should be based on modeling of both radiative transfer and transient heating of human tissues. An adequate computational model should allow prediction of the thermal conversions in the cells of the tissues. A computational analysis based on a general approach developed recently by the authors for indirect heating strategy showed that two-dimensional effects of the radiative transfer are not so important for superficial tumors because of a very high extinction of the incident beam. This enabled us to develop a simplified transient model based on 1-D numerical solution for radiative transfer and 2-D axisymmetrical heat transfer model. A difference between the local temperatures of arterial blood and ambient tissue appears to be also not significant for the soft thermal treatment of superficial tumors. The resulting approximate theoretical model based on 1-D solution for radiative transfer and local thermal equilibrium between blood and tissue makes it possible to study a feedback effect of both thermal and optical properties of partially destroyed human tissues on the parameters of the thermal treatment. It is shown that computational error of the simplified approach for typical superficial tumors is negligible. The numerical study for realistic parameters of human tissues showed that the effects of temperature variation of both thermal and optical properties of the tissues are insignificant. The increase in absorption coefficient of the irradiated healthy tissue with degree of thermal damage also did not have a significant effect on a correct choice of the thermal treatment parameters. However, the role of uncertainty in the local thickness and thermal conductivity of the fat layer may be significant and should be taken into account in thermal treatment of superficial tumors.