Thermal effects of photodynamic therapy on the larynx. Experimental study

Whether cell death in carcinoma of the larynx during photodynamic therapy is due to singlet oxygen formation or mild hyperthermia is not resolved. When various experimental tumors were previously heated within the range of 41 degrees C to 43 degrees C, selective destruction was found. A canine model was used by placing a thermocouple probe into the vocal cord and then varying the total energy (10 to 150 J/cm2), using a 630-nm dye laser; a temperature rise of only 0.5 degrees C to 2.1 degrees C was found. Thus, the thermal effects generated within the larynx (final temperature, 34.9 degrees C to 37.1 degrees C) should be insufficient to act alone in achieving a therapeutic response in either tumor tissue or destruction of normal epithelium.