Applying heat to the prostate gland is not new. In 1921, McCaskey used heat in the form of ultraviolet lamps to treat prostatism, and Corbus used diathermy probes for the same purpose in 1929 (1,2). These therapies were never clinically accepted. In the 1980s, the use of heat to treat BPH regained clinical interest as alternatives to TURP and open prostatectomy were being explored. The modern use of microwaves has been credited to Yerushalmi and associates (3). In 1982, they performed microwave therapy on a patient with prostatic adenocarcinoma and later reported the therapeutic use of microwaves by the transrectal route to treat patients with BPH who were poor operative candidates (3,4).
The first machines studied in clinical trials used the transurethral route in a series of 10 1-hr sessions. These machines used software and instrumentation that allowed only limited and often interrupted delivery of energy to the prostate. Intraprostatic temperatures reached 40-45°C. Patients reported a subjective improvement in symptoms, although an objective improvement of voiding parameters was not observed (5). Histologic studies revealed that prostatic cells were not destroyed, but symptomatic improvement was proposed to be the result of destruction of the a-adrenergic nerve fibers around the prostate, leading to a change in the voiding reflex.
Further research revealed that temperatures greater than 45 °C were necessary to cause coagulative necrosis, protein denaturation, and tissue ablation to reliably destroy prostate cells. These cells would slough away over a period of weeks to months. Increasing the temperature to 47°C further enhanced apoptosis. The introduction of urethral cooling reduced the pain threshold and allowed higher energy to be used, resulting in higher intraprostatic temperatures and tissue destruction. The term hyperthermia was coined to describe treatment using temperatures <45 °C, and thermotherapy was used to describe therapy with temperatures >45 °C.
As prostate tissue was destroyed more reliably, the time of therapy was decreased. Antennae were improved to provide concentric distribution of heat. Heat distribution now generally follows the anatomic borders of the transition zone, the main source of adenomatous tissue. The use of thermotherapy resulted in significant improvement in both objective and subjective measures. Histologic examination of specimens revealed cell destruction but no reliable cavitations. Patients invariably had severe prostatic edema and urinary retention requiring the use of a urinary catheter, which became standard practice after TUMT.
To further improve outcomes, high-energy thermotherapy was introduced. Temperatures greater than 70°C were reached, causing thermoablation of prostatic tissue. Unlike with thermotherapy, prostatic cavities were observed on histologic sections with high-energy thermotherapy, resulting in greater improvement in symptom and objective parameters. However, patients did not notice an immediate improvement after high-energy thermotherapy but rather had a gradual change over a period of months.
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