Nd: YAG laser thermocoagulation of the prostate: the barbecue effect

To determine systematically the depth of coagulation necrosis induced during Nd: YAG laser irradiation in the canine prostate model, and to define the correlation of laser dose with depth of the lesions.

We investigated the effect of various dosimetries on prostatic tissue of 17 mongrel canines using laser power in the range of 8 to 60 watts (W) at varying exposure times, from 20 to 300 seconds (S). Applied energy ranged from 1,000 to 5,500 Joules (J).

Three distinct features were observed. First, deep coagulation necrosis was induced only with laser regimens of > or = 2,100J, suggesting that there is a threshold of energy that must be overcome in order to achieve significant coagulation depth. Second, the deepest coagulation necrosis was achieved with a low power slow-heating regimen (15W X 180S). Tissue surface changes appeared to be responsible for the reduced depth of coagulation necrosis seen with higher power regimens (> 20 W). Third, increasing the energy above 3,600J did not augment the depth of coagulation, suggesting that a steady state for temperature distribution is reached at that rate of heating.

Our study suggests that in the canine prostate, a low power slow-heating regimen of 15W X 180S may yield larger volumes of coagulation necrosis than other regimens.