Background and objective: Interstitial laser coagulation is an experimental treatment to eliminate solid tumors such as hepatic metastases. The pattern of light emission from the fiber tip is probably an important factor in determining the size and shape of a lesion. A heat-resistant cylindrical light diffusing tip of 2 cm length was developed for this application. We performed an in vitro study to compare this diffusing-tip with a bare-tip fiber.
Study design/materials and methods: Fiber ends were positioned between two porcine liver slabs (37 degrees C) and Nd:YAG laser light (1064 nm) was guided through either fiber with an output of 3-9 W and exposure times of 6-18 minutes.
Results: Lesions produced by the cylindrical diffuser tip were significantly larger and more predictable. With the diffuser tip, lesions up to 36/23 mm (length/width) could be produced at 7 W and 9 min without any central charring. The maximum size of lesions produced with the bare-tip fiber was 32/20 mm at 6 W for 9 min with massive charring.
Conclusions: The results indicate that at optimal laser settings, the diffuser tip produces a larger coagulation volume than a bare-tip fiber. For clinical application, cylindrical diffusing fibers should be used with a diffusing length adapted to the diameter of the tumor.