Experimental laser interstitial thermotherapy in ex-vivo porcine tissue at 980 nm and 830 nm

The purpose of these experiments was to compare the temperature increase in ex-vivo porcine mammary chain tissue as a breast tissue model during interstitial laser irradiation with diode lasers emitting at 980 nm and 830 nm. Both wavelengths were delivered at 4.0 W for 10 minutes through a diffusing fiber inserted into ex-vivo porcine tissue. The temperature was measured with a set of 15 thermocouples placed 5, 10, and 15 mm from the fiber axis. The initial rate of temperature increase 5 mm away from the fiber tip was higher at 980 nm (0.12 to 0.20 degree(s)C/s) than at 830 nm (0.10 to 0.16 degree(s)C/s). At 10 mm and 15 mm (areas with less radiation), the rate was smaller than at 5 mm (less than 0.06 degree(s)C/s at 10 mm and less than 0.02 degree(s)C/s at 15 mm) for both wavelengths with no significant difference between the 980 nm and 830 nm radiation. The temperature increase at 5, 10 and 15 mm away from the fiber tip after 10 minutes of irradiation was higher at 980 nm (36 to 45 degree(s)C at 5 mm, 14 to 30 degree(s)C at 10 mm and 9 to 17 degree(s)C at 15 mm) than at 830 nm (27 to 33 degree(s)C at 5 mm, 11 to 17 degree(s)C at 10 mm and 8 to 9 degree(s)C at 15 mm) after 10 minutes. These results were found to be highly dependent on tissue composition (muscle vs. fatty tissue).