Depth of penetration of the neodymium:yttrium-aluminum-garnet laser in the human prostate at various dosimetry.

Objective: To determine depth of thermal penetration by the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser at various dosimetry in the human prostate and to compare results of two techniques of laser application, single spot versus whole tissue photoirradiation.

Methods: Twelve men with Stage T2 (B) cancer of the prostate consented to laser prostatectomy immediately prior to a planned radical prostatectomy. In the first 3 patients (group I) the prostate was treated with the Nd:YAG laser in one spot area of each lobe. The next 9 patients underwent photoirradiation of all endoscopically visible tissues on one side of the prostate at different dosimetries: 60 W at sixty seconds (group II), 50 W at sixty seconds (group III), and 40 W at ninety seconds (group IV). Depth of laser penetration was measured from both histologic and gross evaluations of removed specimens within twenty-four hours.

Results: Thermal necrosis in group I showed an inconsistent depth of penetration even with the same amount of laser energy. Groups II, III, and IV all demonstrated clearly demarcated areas of thermal necrosis. Group II showed the greatest depth of laser effect among all groups, with a mean depth of 1.75 cm. No laser effect is detected near the true capsule of the prostate on any specimen.

Conclusions: High dosage laser energy application at 60 W and sixty seconds of pulse duration with the whole tissue treatment provide the greatest depth of penetration in the human prostate while maintaining safety for the capsular area.