Neodymium:YAG laser irradiation of the canine prostate provides an experimental model for the study of the laser-tissue interaction in laser prostatectomy. Prostate irradiation was undertaken using right-angle-firing laser fibers through an open suprapubic cystotomy, and the procedure was monitored by video endoscopy via a perineal urethrostomy. The effects of popcorn and surface carbonization on intraprostatic heating profiles were determined by interstitial thermometry. We found that popcorn reduced intraprostatic temperatures but that continued irradiation resulted in the restoration of heating. Carbonization resulted in the loss of heating ability deep in the prostate. These observations allow the urologist to understand the thermal implications of observed surface change and to modify lasing parameters during surgery to obtain the desired laser-tissue interaction.
Laser prostatectomy is an ever-increasing procedure due to its ease of performance, low morbidity, and efficacy [2,5,8,10]. The ability to deliver Nd:YAG energy to the prostate using a variety of right-angle-deflecting fibers and contact probes has resulted in many approaches to the destruction of prostate tissue. Nd:YAG energy can be used to coagulate prostatic tissue under ultrasound guidance (TULIP; transurethral ultrasound-guided laser-induced prostatectomy) [11] or visual guidance (VLAP; visual laser ablation of the prostate) [3,8] or by the placement of interstitial light guides (ITT; interstitial thermotherapy) [12,13]. In addition, acute tissue vaporization can be accomplished by some free-beam fibers and contact applicators [4,6,14].
The amount of thermal damage caused by the laser is due to the combination of light absorption, scatter, transmission, and reflection. Alterations in these prostatic-tissue optical properties occur continuously during laser irradiation. Surface blanching is related to protein denaturation at temperatures above 65 ยฐ C, and by 90ยฐ-100ยฐC there