Photoselective vaporization prostatectomy: experience with a novel 180 W 532 nm lithium triborate laser and fiber delivery system in living dogs.

PURPOSE: We studied vaporization parameters, and anatomical and histopathological outcomes of photoselective vaporization of the prostate with the novel GreenLight™ XPS™ 180 W, 532 nm lithium triborate laser and MoXy™ fiber in a survival model of living dogs. We compared these findings with those of the existing GreenLight HPS™ 120 W 532 nm lithium triborate laser photoselective vaporization of the prostate in living dogs. MATERIALS AND METHODS: Eight dogs underwent antegrade photoselective vaporization of the prostate with the 180 W laser delivered through a new 750 µm (vs the existing 600 µm core diameter), 50% larger, spot sized, side firing fiber. Four dogs were sacrificed 3 hours and 8 weeks postoperatively, respectively. We recorded laser energy and time. Prostates were sectioned, measured and histologically analyzed after hematoxylin and eosin, triphenyltetrazolium chloride or Gomori trichrome staining and compared with a normal control. RESULTS: Photoselective vaporization of the prostate with the 180 W laser bloodlessly created a 76% larger cavity (mean 11.8 vs 6.7 cm(3), p = 0.014), vaporized tissue at a 77% higher rate (mean 2.3 vs 1.3 cm(3) per minute, p = 0.03) and did so in 37% less time per volume vaporized (0.5 vs 0.8 minutes per cm(3), p = 0.003). Hematoxylin and eosin, and triphenyltetrazolium chloride staining histologically revealed a 33% thicker mean coagulation zone vs that of 120 W laser photoselective vaporization of the prostate (2.0 ± 0.4 vs 1.5 ± 0.3 mm, p <0.005). In prostates healed for 8 weeks postoperatively hematoxylin and eosin, and Gomori trichrome staining showed re-epithelialized cavities with negligible submucosal fibrosis compared with a normal prostate. CONCLUSIONS: GreenLight XPS 180 W 532 nm lithium triborate laser photoselective vaporization of the prostate with the MoXy fiber has a significantly higher vaporization rate and speed with a deeper hemostatic coagulation zone but favorable tissue interaction and healing equal to those of HPS 120 W laser photoselective vaporization of the prostate in dogs.

Quantitative evaluation of high power effect on 532 nm laser vaporization of bovine prostate in vitro.

PURPOSE: We investigated the effect of 120 to 200 W high power levels on in vitro vaporization of bovine prostate using a custom-made 532 nm lithium triborate laser system. MATERIALS AND METHODS: Light (532 nm) delivered through a newly designed 750 microm core diameter side firing prototype fiber vaporized 114 bovine prostate tissue specimens in saline at 20C using a 2-dimensional scanning system. Various conditions were tested, including 120 to 200 W power, 1 to 5 mm working distance and 2 to 8 mm per second treatment speed. RESULTS: Regardless of treatment speed 180 W was the optimal power to maximize tissue vaporization efficiency by removing 80% more tissue than at 120 W. At 120 and 180 W laser light vaporized tissue more efficiently at a 4 mm per second treatment speed and vaporized equally efficiently at up to 3 mm working distance. At the slowest treatment speed the mean thickness of the coagulation zone at 180 W was 20% thicker than at 120 W (1.31 vs 1.09 mm) but still thin, comparable to previous findings of 1 to 2 mm. CONCLUSIONS: In vitro the 532 nm lithium triborate laser showed that 180 W is the optimal power to maximize tissue vaporization efficiency with enhanced coagulation characteristics. These desirable outcomes must be validated in vivo.

In vitro investigation of wavelength-dependent tissue ablation: laser prostatectomy between 532 nm and 2.01 microm.

BACKGROUND AND OBJECTIVE: Over a decade, laser prostatectomy has been performed to effectively treat benign prostate hyperplasia (BPH) with low post-operative complications. In this study, two laser wavelengths conventionally used for BPH treatment were compared to characterize the outcomes of in vitro tissue ablation. STUDY DESIGN/MATERIALS AND METHODS: Two lasers with wavelengths including 532 nm (Q-switched) and 2.01 microm (continuous wave) were employed to ablate porcine kidney tissue in vitro. Ablation performance was evaluated by varying applied power, treatment speed, and fiber working distance. Optical transmission was measured as a function of working distance and compared with the corresponding ablation volume. Coagulation depth was quantified from gross tissue examination, and histology analysis confirmed coagulation features for both wavelengths. RESULTS: Five hundred thirty-two nanometers yielded up to 30% (P<0.005) higher ablation efficiency than 2.01 microm. Regardless of wavelength, ablation rate increased with power and was maximized at treatment speed of 4 mm/seconds. A comparable ablation depth was found between the two wavelengths, but 532 nm generated relatively wider (up to 30%; P<0.005) craters. Both optical transmission and ablation volume revealed that energy loss by strong water absorption compromised ablation efficiency generated by 2.01 microm. Gross tissue and histology examination demonstrated that 532 nm created a thin coagulation zone whereas 2.01 microm induced approximately 20% (P<0.005) more thermal injury in association with carbonized tissue surface. CONCLUSIONS: Due to more light scattering and effective thermal confinement, 532 nm induced more efficient tissue ablation with a smaller coagulative necrotic zone. Comparable ablation depth may enable a potential tissue incision technique with 532 nm, possibly allowing both tissue removal and biopsy intraoperatively.