Hyperthermia treatment using a computer-controlled Nd:YAG laser system in combination with surface cooling

An Nd:YAG laser hyperthermia system was used to induce hyperthermia in chemically-induced rat mammary adenocarcinomas. Excessive heating of the surface tissue limits the depth of heating during laser-induced hyperthermia. To determine whether surface cooling would allow heating of deeper tissues, treatment surfaces were cooled using two different techniques. (1) an IV drip in conjunction with oxygen flow directed toward the surface, and (2) moisture saturated oxygen flow from a nebulizer. The laser was interfaced to a computer and a thermometer that provided feedback to maintain the tumor temperature between 43.2- 43.5 degree(s)C. The thermocouple was placed in the base of the tumor and its temperature was used via the feedback system to control laser exposure. All tumors were 1.0 to 2.0 cm in diameter. While both cooling techniques lowered the surface temperature effectively, nebulizer technique was preferred due to better control of surface cooling and less fluid accumulation around the treatment area. Nd:YAG laser hyperthermia delivered in conjunction with surface cooling using the nebulizer technique produced efficient heating of rat mammary adenocarcinomas to an approximate depth of 15 mm without overheating the surface tissue.