Presence of coagulative necrosis gradient in human prostate following a short Nd-YAG laser irradiation

Background and objective. The human prostate is a glandular organ that has intervening fibromuscular elements. The objective of this study was to evaluate the thermocoagulative effect on the different components of the organ exposed to Nd-YAG laser irradiation using a new ITT optic fiber design (Interstitial Thermal Therapy). Study Design/Patients and Methods. Twelve fresh transvesical prostatectomy specimens were irradiated ex-situ at 4 to 6 sites using an ITT fiber with laser energies ranging from 900 to 4500 joules (j) applied at times ranging from 60 to 300 seconds corresponding to 10 to 15 watts. The specimens were serially sectioned to include the proximal, mid and distal regions of the centrally coagulated channel. An ocular grid was utilized to measure the radius (r) of thermal injury from the margin of the centrally coagulated channel to the furthermost detectable area of thermally induced changes. Results. The maximal extent of thermal injury was seen at the mid-length of the irradiated channel at energy of 2700 j (15 w/180 sec). The fibromuscular compartment of the prostate was more affected (r = 855 μm) and showed more interstitial vacuolization and charring than the adenomatous one (r = 495 μm). Utilization of higher energy doses did not significantly alter the depth of injury but did reduce the extent of interstitial vacuolization of both components. Conclusion. The study indicates that the extent of laser induced coagulative necrosis depends on the histologic architecture of the prostate and also varies in extent along the length of the channel surrounding the fiber.