Evaluation of thermal response of the prostate to ND:YAG laser photocoagulation

Abstract

Laser treatment of Benign Prostatic Hyperplasia (BPH) has gained considerable attention as a safe and effective alternative to conventional Transurethral Resection of the Prostate (TURP). The present study tries to find the influence of the treatment parameters (the rate of tissue heating and the tip geometry) on the thermal effects of laser interaction with prostatic tissue and the extend of coagulation necrosis. Thermal and optical sensors were connected to instruments and personal computers to develop an integrated system for temperature and light measurement inside the prostate. Two types of fiber tips were investigated. In vivo studies were performed on canine prostates using side firing fibers to measure the temperature and light distribution induced by the slow heating and the fast heating. Temperature and light information obtained during this study were correlated to the cysthoscopic image and extend of tissue damage. It was observed that less surface damage coupled with a longer heat conduction time assures a higher depth of coagulation necrosis in the case of slow heating. In the second part of the study, we tested the feasibility of delivering a maximum of 10OW of laser power through diffusing tips, which distribute the light over the entire surface of the urethra along the tip length. Both in vitro and in vivo studies were performed. The coagulation depths and temperature distribution produced by different combinations of power and exposure time were examined. It was observed that power densities much lower than those of a side firing beam are sufficient to produce the same depth of coagulation necrosis. The diffusing tips are capable of uniformly distributing high power laser radiation and producing deep, long and symmetric zones of coagulation necrosis around the urethral lumen while minimizing total irradiation time.