Investigation on safety aspects of forward light propagation during laser surgery

During laser treatment of prostate, urological surgeons occasionally experience fiber-cap failure due to concentration of thermal stress on the fiber tip. Upon the cap breakage, laser light becomes forward-propagating and may adversely affect the bladder tissue such as perforation. The purpose of the current study was to identify any bladder perforation with forward-propagating laser light (λ = 532 nm) at 80 and 120 W with an assumption of fiber-cap failure. Perforation time was measured and compared in terms of fiber distance. The results showed that 80 and 120 W perforated the tissue up to 2 and 2.5 cm, respectively with perforation threshold of 17.2 kW/cm(2), and the minimum perforation time was approximately 7 s. No perforation occurred at the distance of 3 cm for 1-min irradiation at both power levels, but severely carbonized lesions were generated around the irradiated tissue. Although equivalent ablation speed was found between the two power levels, 120 W created up to 20 % wider craters regardless of fiber distance. With consideration of dense collagen fibers in bladder structure and long surgical distance, direct incidence of laser perforation on bladder wall could be unlikely to happen upon fiber-cap failure during laser surgery.