Laser treatment of benign prostatic hyperplasia : dosimetric and thermodynamic considerations

Abstract

Benign prostatic hyperplasia (BPH) is the most commonly occurring neoplastic disease in the aging human male. Currently, surgical treatment of BPH is the primary therapeutic method. However, due to surgical complications, less invasive methods of treatment are desirable. In recent years, thermal coagulation of the hyperplastic prostate by a laser has received a considerable amount of attention. Nevertheless, the optimum laser irradiation parameters that lead to a successful and safe treatment of BPH have not been determined. This dissertation studies the physics of laser coagulation of prostate from both basic science and practical perspectives. Optical properties of prostatic tissue are determined over a spectrum of wavelengths. Knowledge of these properties allows for selection of appropriate laser wavelengths and provides a basis for performing dose equivalency studies among various types of lasers. Furthermore, knowledge of optical properties are needed for development of computer simulation models that predict the extent of thermal injury during laser irradiation of prostate. A computer model of transurethral heating of prostate that can be used to guide the clinical studies in determining an optimum dosimetry is then presented. Studies of the effects of non-laser heating devices, optical properties, blood perfusion, surface irrigation, and beam geometry are performed to examine the extent of heat propagation within the prostate. An in vitro model for transurethral laser irradiation of prostate is also presented to examine the effects of an 810 nm diode laser, thermal boundary conditions, and energy deposition rate during Nd:YAG laser irradiation. Results of these studies suggest that in the presence of laminar irrigation, the convective boundary condition is dominated by thermal diffusion as opposed to the bulk motion of the irrigation fluid. Distinct phases of thermal events are also identified during the laser irradiation. The in vivo studies of transurethral laser irradiation of prostate in canine models are also performed to search for an optimum dosimetry that will result in a maximum zone of coagulation necrosis.