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Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of
D Protsenko1, J H Torres, P Chakrabarti
1Department of Surgery, The University of Texas Medical Branch at Galveston, Texas 77555, USA.
Objectives:
Currently, various side-emitting optical fibers with different tip geometry are used transurethrally to deliver laser radiation for treatment of benign prostatic hyperplasia (BPH). Since fiber tip design could profoundly affect the size and profile of the emitted laser beam, and consequently the tissue response and the extent of tissue coagulation, we evaluted commercially available fibers in regard to their optical characteristics and their ability to coagulate tissue in a controlled experimental setting.
Methods:
Thirteen fibers manufactured by different companies and clinically used at the present time were tested using a surgical neodymium: yttrium-aluminum-garnet laser. The profile of the laser beam delivered via each fiber was imaged on a CCD camera at various distances and evaluated by means of a laser beam analyzer. Beam divergence angle was then calculated for each tip. Tissue coagulation effects were assessed by irradiating samples of beef muscle immersed in water at 37 degrees C. The fiber tip was kept 2.5 mm away from the tissue and irrigation was maintained at flow rate of 350 to 400 cc/min during irradation. Laser powers of 20, 40, and 60 W were used for 180, 90, and 60 seconds, respectively, delivering a total energy of 3600 J.
Results:
The results of the optical evaluation divided the fibers into two major groups: broad beam with large divergence angle and narrow beam with small divergence angle. Statistical analysis of the data (using analysis of variance) showed that volumes of coagulated tissue were significantly larger for broad beam fibers than for narrow beam fibers (1.15 +/- 0.32 versus 0.89 +/- 0.34 cm 3; P < 0.05). Also, significantly larger volumes were obtained for 20 W when compared with 60 W (1.08 +/- 0.43 versus 0.88 +/- 0.27 cm 3; P < 0.05).
Conclusions:
The laser power density delivered by individual fibers to the prostate tissue may vary significantly, thus greatly affecting the extent of tissue coagulation. Therefore, irradiation parameters must be optimized for each fiber type.