Temperature measurements and histology of the canine prostate during transurethral hyperthermia

Intraprostatic temperature measurements during transurethral hyperthermia at 44.5C were obtained in 5 dogs. Temperatures were also recorded in the bladder neck wall and the rectal wall. After completion of the temperature measurements, hyperthermia was continued for 3 hours. The prostates were then removed and taken for histologic examination immediately after hyperthermia and 1 week and 1 month later. The mean temperatures obtained in the 5 canine prostates were 44.5 +/- 0.4C at the heating electrode; 43.8 +/- 0.4C at a distance of 3 mm. from the electrode; 42.6 +/- 0.5C, 40.8 +/- 0.4C and 39.4 +/- 0.5C, 6, 9 and 12 mm. from the heating electrode, respectively, in the right, prostatic lobe. Similar temperatures were measured in the left lobe. The thermal gradient in the prostatic tissue was therefore about 4C per 1 cm. On histology, hemorrhagic necrosis of the prostatic tissue adjacent to the urethra was found. These histologic changes were found as much as 5 mm. from the heating antenna (where the temperatures measured were above 43C). The findings of our study may have major clinical importance. We found that thermal energy above 43C provides enough penetration to cause tissue damage and be clinically effective in most patients, while the thermal gradient around the heating electrode of 4C per 1 cm. is steep enough to confine histologic damage within the prostate.