LASER PHOTOCOAGULATION OF PROSTATE - INFLUENCE OF DOSIMETRY

Background and Objective: Recently, increasing enthusiasm has been sho wn for application of lasers for the treatment of benign prostate hype rplasia (BPH). However, little is known about the thermodynamics of pr ostatic tissue response during laser irradiation and how the treatment outcome can be optimized. Our objective was to conduct a systematic s tudy of the influence of exposure parameters on the extent of tissue c oagulation and to determine the effects of rate of tissue heating on l esion size by comparing the tissue response to high laser power rapid heating vs. low laser power slow heating. Study Design/Materials and M ethods: Nd:YAC; laser irradiation of prostate was performed in 15 mong rel canines, using an incident power of 15, 30, or 50 Watts (at the fi ber tip) and an exposure time varying from 30 to 300 seconds. The lase r beam was delivered via a Urolase side-emitting catheter. The tissue response was compared based on gross as well as histological evaluatio ns of thermal lesions. Results: The depth of coagulation necrosis incr eased as the laser power was reduced from 50 W to 30 W and further to 15 W while the total delivered energy was kept constant at 2,700 J by adjusting the exposure time. The difference between the three heating rates was more dramatic when the estimated volume of coagulated tissue was considered. Increasing the irradiation time for the low power (15 W) from 180 to 300 seconds resulted in enlarging the coagulated volum e by a factor of 1.6. However, for high power (50 W), increasing the e xposure time from 54 to 90 seconds resulted in increasing the coagulat ed volume by a factor of 1.2. Conclusion: This study suggests that a s low heating regimen yields larger volumes of coagulation necrosis than the currently used rapid heating approach. (C) 1995 Wiley-Liss, Inc.