A minimally invasive prostatic interstitial temperature-mapping technique is described that supplies accurate, detailed information on thermal doses delivered to precisely localized tissue sites. The technique employs a comparatively large numbers of thermosensors, highly accurate placement of those thermosensors at specified three-dimensional coordinates, fiberoptic technology that avoids significant interaction between the thermosensors and the applied microwave field, and continuous temperature readout. Biplane ultrasound imaging and fluoroscopy were used to ensure stereotactic accuracy of thermosensor placement. The technique was applied in 15 patients with benign prostatic hyperplasia (BPH) undergoing a 1-hour microwave thermal treatment session. The thermal mapping procedures and microwave treatment were generally well tolerated. The mean maximum temperature in the prostate and periprostatic tissue (57.9 ± 1.9°C) was significantly higher (P < 0.001) by more than 18°C than that in either the urethra (39.6 ± 0.9°C) or the rectum (40.8 ± 1.7°C). In a representative patient, microwave treatment resulted in stable elevation of temperature 5 mm radially from the urethra that averaged 66.0 ± 0.1°C. At 10 mm from the urethra, the temperature averaged 50.5 ± 0.1°C. Urethral and rectal temperatures remained at innocuous levels. In conjunction with pathologic studies, this interstitial thermal mapping method should prove useful in defining the optimal thermal doses for microwave therapy. The method should also find uses in evaluating different microwave treatment systems, which can vary markedly in thermal performance, as well as other modalities that apply heat to prostatic tissue.
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