Comparison of 980- and 1064-nm wavelengths for interstitial laser thermotherapy of the liver.

Objective: Interstitial laser thermotherapy (ILT) of liver tumors is generally performed using neodyium yttrium-aluminium-garnet (Nd-YAG) lasers. More versatile diode units, developed predominantly for other clinical applications, may be equally suitable for ILT. This study compares the efficacy of diode and Nd-YAG lasers in achieving maximum tissue necrosis, at low power, in a murine model.

Methods: Thermal ablation was induced in the liver of CBA strain mice by diode (980-nm wavelength) and Nd-YAG (1064-nm wavelength) lasers using 400-microm diameter bare fibers. Treatment time prior to tissue charring was determined for both lasers at a power output of 2 W. Tissue temperature was recorded upon completion of therapy 3 mm from the fiber insertion site. The maximum diameter of necrosis was accurately assessed by nicotinamide adenine dinucleotide (NADH) diaphorase tissue staining.

Results: Maximum diameter of tissue necrosis prior to charring occurred at 20 s (40 J) with the diode laser compared to 50 s (100 J) with the Nd-YAG laser. The maximum diameter of necrosis (mean [SEM]) produced by the diode laser, 5.9 mm (0.14), was equivalent to the necrosis induced by the Nd-YAG laser, 5.9 mm (0.14) (p = 0.963). Tissue temperature 3 mm from the fiber application site immediately following ILT in the diode laser group, 40.8 degrees C (0.93), was not statistically different than that of the Nd-YAG laser group, 39.0 degrees C (0.86) (p = 0.452). Tissue charring consistently prevented treatment beyond 20 s at 2W by the diode laser.

Conclusions: Low power ILT with diode and Nd-YAG lasers achieves equivalent maximal necrosis when applied to the liver by a bare fiber. Treatment time to produce maximal necrosis is however significantly shorter with the diode laser.