DOSIMETRY STUDIES UTILIZING THE UROLASE RIGHT-ANGLE FIRING NEODYMIUM-YAG LASER FIBER IN THE HUMAN PROSTATE

Background and Objective: Until recently, little or no objective data have been available to support either the choice of power setting or t he timing of laser applications to achieve optimal tissue ablation in the human prostate. The objective of this study was to define quantita tive dosimetry curves for the Urolase right angle laser fiber in human prostates. Study Design Materials and Methods: Transurethral Neodymiu m:YAG laser application was performed with the Urolase right-angle las er fiber in adult human prostates prior to planned radical surgery. De pth and volume of prostatic tissue coagulation for single, continuous laser applications were measured at variable power settings from 20 to 60 watts while holding total energy delivery constant. Then, holding the power setting constant at 40 watts, the extent of tissue coagulati on was measured for variable treatment times from 60 to 120 seconds.Re sults: Peak tissue coagulation was observed at 40 watts up to a maximu m of 14 mm tissue penetration and 4.23 cc volume coagulated following a single spot laser application. The mean depth of tissue coagulation at 40 watts power setting was 13.5 mm, with a mean volume of tissue co agulation of 3.68 cc, The mean depth of tissue penetration at 40 watts was more than 25% greater than that observed at 60 watts, and the mea n volume of tissue coagulation was 190% greater than that observed at 60 watts. As treatment time was increased from 60 to 90 seconds, exten t of tissue coagulation increased significantly. However, beyond 90 se conds continuous laser application at 40 watts, a plateau in tissue ef fects was observed, with minimal increase in tissue coagulation betwee n 90 and 120 seconds. Histologic examination of prostates removed acut ely showed heat-induced damage to both stromal and glandular epithelia l elements in laser-treated areas. At 1 year, the prostatic urethra wa s lined with a normal transitional epithelium, and mild periurethral f ibrosis with focal squamous metaplasia was seen. Conclusion: Using the Urolase right-angle laser fiber, this study suggests that 40 watts po wer setting and 90 seconds continuous application time with a Neodymiu m:YAG laser source represent optimal treatment parameters to maximize prostatic tissue coagulation. (C) 1996 Wiley-Liss, Inc.