The Effect of Laser-Fiber Sweeping Speed on the Efficiency of Photoselective Vaporization of the Prostate in anEx VivoBovine Model

Abstract

Recommendations for efficient photoselective vaporization of the prostate (PVP) include a side-to-side rotational laser-fiber "sweeping" motion, yet scientific study of this technique is lacking. We investigated whether the speed of laser-fiber sweeping affects tissue vaporization efficiency. PVP was performed using the 120-W GreenLight high-performance system. Video analysis of a surgeon performing PVP was carried out to identify sweeping speeds used clinically. PVP efficiency was subsequently tested at four different sweeping speeds using two manipulations of an ex vivo bovine prostate model, including (1) excised prostate tissues (n = 40) in a vaporization chamber equipped with motorized laser-fiber movements; (2) retrograde endoscopic vaporization (n = 80) within whole lower urinary tracts. Vaporized cavity sizes and coagulative margins were measured by liquid-paraffin molding and histologic cross-sectioning approaches. Video analysis of clinical PVP showed wide variability in sweeping speed, mostly ranging between 0.5 and 2.0 (mean 1.50) sweeps/second. Using either manipulation of the ex vivo bovine prostate model described above, PVP at lower sweeping speeds (0.5 and 1.0 sweeps/second) removed significantly more tissue (up to twofold) compared with higher sweeping speeds (1.5 and 2.0 sweeps/second), with significant albeit minimal reductions in coagulation margins. In this ex vivo prostate model, our results suggest that vaporization efficiency is compromised with faster laser-fiber sweeping. This finding counters principles of traditional transurethral resection of the prostate, in which faster axial movement toward the surgeon removes tissue more efficiently. This study highlights that PVP technique can be tested in a scientific manner, identifying optimal parameters for achieving maximal tissue vaporization efficiency.