Detailed interstitial temperature mapping during treatment with a novel transurethral microwave thermoablation system in patients with benign prostatic hyperplasia

Purpose: To delineate in detail the temperature changes in the prostate gland and adjacent structures during treatment with a newly designed microwave thermoablation system in patients with benign prostatic hyperplasia (BPH). Materials and Methods: Microwave thermoablation treatment was administered to 22 BPH patients at two centers in the U.S. and Argentina using the Urologix Targis® targeted transurethral thermoablation system. Continuous temperature measurements were made with widely spatially dispersed fiber optic thermosensors at 11 to 24 prostatic sites in each patient using a recently described accurate stereotactic method. Urethral and rectal temperatures were also measured. Results: Treatment using the microwave thermoablation system resulted in marked elevation of intraprostatic temperatures to as high as 80C in some patients with little or no elevation of urethral or rectal temperatures. Average temperature increased with radial distance from the urethra to a peak at 5 to 7 mm. and declined exponentially at greater distances. Higher maximum intraprostatic temperatures in individual patients were associated with a larger zone, up to 24.0 mm. in radius, of prostatic tissue exposed to thermoablative temperatures of 45C and higher. Along the longitudinal axis of the microwave treatment catheter, thermoablative temperatures were confined to a zone of 11.5 mm. from the microwave antenna midpoint apically and 11.3 mm. basally, that is, a range shorter than the length of the treatment catheter's microwave antenna (2.8 to 3.5 cm.). The mean temperature in the posterior sector of the prostate gland during treatment (43.6C; 95% CI, 41.1 to 46.1C) was significantly lower (p <0.05) by 6.7C than that in the anterolateral prostate (50.3C; 95% CI, 48.3 to 52.3C), as a consequence of the preferential heating design of the treatment catheter. Intraprostatic mean temperature during treatment, as measured at all thermosensor sites without respect to spatial location, was 47.1C (95% CI, 44.2 to 50.0C), a value significantly higher (p <0.05) than that measured in the urethra (39.6C; 95% CI, 36.6 to 42.6C) or rectum (37.7C; 95% CI, 36.7 to 38.7C). There was a strong correlation between the temporal pattern of fluctuation in urethral temperature and that of prostate temperature (r = 0.83; p <0.001) during treatment. Conclusions. Treatment with the microwave thermoablation system fulfilled the requirements for an effective and safe microwave-based BPH treatment modality by exposing obstructive tissue to high temperatures without endangering vulnerable adjacent tissues.