| Abstract: | Background and Objective: The purpose of this study was to determine the geometrical development of a coagulated zone in the canine prostate during free beam side fire Nd: YAG laser coagulation. Study Design/Materials and Methods: A series of 10 male dogs underwent endoscopic prostatic Nd: YAG fixed position laser coagulation through a suprapubic cystotomy using a right-angle deflecting delivery catheter (Microvasive, Boston, MA) at times varying from 10 to 120 seconds at 30 watts. In addition, two dogs underwent lasing by pulling the catheter at 1 mm/s in four quadrants. Acute gross and microscopic pathology specimens were prepared and the lesion shape and volume determined. Results: Analysis of the coagulated volume showed that during the initial 15 seconds of lasing, the zone of coagulation approximates a sphere centered on the urothelium opposite the laser fiber. However, as lasing progressed, the lesion changed from a sphere to an expanding ellipse. This changing geometry can be explained by the absorption and scatter characteristics of the laser and the temperature equilibrium that is established within the prostate. Conclusion: An understanding of this time-dependent geometrical shift from a sphere to an ellipse allows the surgeon to supplement the fixed protocols for lasing at certain positions for given amounts of time. Specific plans can then be established for tissue at the bladder neck, apex, anterior stroma, floor, and irregular prostatic regrowth. © 1995 Wiley-Liss, Inc. |
