Transurethral microwave thermotherapy of 340 patients treated at our center for benign prostatic hypertrophy shows the importance of the role played by two thermoregulation processes during the procedure. The first one is artificial and automatically driven by the machine (the power output and cooling rate are adjusted to the urethral and rectal temperature safety thresholds). The second one is natural thermoregulation; the latter is species specific, organ specific,zone specific and even cell specific. Thermoregulation variability is linked to the geometry of the gland, vessel distribution, histology and tissue conductivity. This variability has been demonstrated by interstitial thermometry and histological study. Interstitial thermometry was performed during treatment in 30 dogs and 35 patients; a histological study of prostate specimens was performed 1-12 weeks after treatment in 30 dogs and 15 patients. The human prostate is more resistant to heat than the dog prostate of a comparable volume and treated with the same thermal dose. The prostate of a young patient requires a higher thermal dose than that of an old patient with the same prostate volume in order to achieve a comparable intraprostatic temperature,probably due to a more viable blood supply. The transition zone is more sensitive to heat than the peripheral zone, as demonstrated by temperatures recorded at the same distance from the antenna of up to 60 versus 42 °C,respectively. Acinar cells seem to be more resistant to heat than smooth muscle cells when exposed to the same temperature level, as demonstrated by microscopic examination at the periphery of the treated area. We can conclude that increases in the thermal dose can only be safely achieved by accurate management of both the natural and artificial thermoregulation processes.

Keywords:
Prostate, Microwaves, Thermoregulation, Thermotherapy
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1993
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