Laser vaporization of bovine prostate: a quantitative comparison of potassium-titanyl-phosphate and lithium triborate lasers.

Purpose: We compared the outcomes of in vitro vaporization of bovine prostate using the lithium triborate GreenLight HPS and the GreenLight KTP PV photoselective vaporization laser.
Materials and Methods: A total of 96 specimens of bovine prostate tissue in saline at 20C were vaporized with a 2-dimensional scanning system using a side firing fiber emitting a 532 nm wavelength at 80 W using the KTP laser, and at 80 and 120 W using the HPS laser at a working distance of 0.5 to 5 mm and a treatment speed of 2 to 8 mm per second. Dimensions of the vaporized tissue and resultant lesions were assessed.
Results: At a minimum working distance of 0.5 mm and a treatment speed of 4 mm per second (determined by optimum vaporization volume/energy use) the HPS laser at 80 and 120 W vaporized 50% and 100% more tissue, respectively, than the KTP laser at the customary 80 W. At the same treatment speed the HPS laser vaporized equally efficiently at up to 3 mm working distance at each power level, whereas the KTP laser lost efficiency at working distances beyond 0.5 mm. The 2 lasers vaporized more tissue at slower (longer lasing) treatment speeds but even at the slowest treatment speed mean thickness of the coagulation zone with the HPS laser at 80 and 120 W was comparable to that of the 80 W KTP laser (0.80 and 1.07 mm, respectively, vs 0.81).
Conclusions: In vitro the lithium triborate GreenLight HPS 120 W laser vaporizes bovine prostate far more efficiently than the KTP photoselective vaporization laser but coagulates it equally well. These favorable outcomes must be validated in vivo.