Background and purpose: The likelihood of success of thermoablation of prostatic hyperplasia depends on delivering an optimal thermal dose, but data on the temperatures achieved with these methods are few. We sought to develop a noninvasive method for monitoring intraprostatic heat distribution.
Patients and methods: Thirteen patients ranging from 50 to 76 (mean 61.3+/-8.1) years were enrolled in this study, all of whom had evidence of obstruction by uroflowmetry and pressure-flow studies. The mean total volume of the gland was 40.3+/-13.1 cc, while the mean adenoma volume was 20.4+/-10.1 cc, as estimated by preoperative transrectal ultrasonography. All the patients were treated with the Urologix Targis device for at least 45 minutes. Continuous temperature mapping was performed during the therapy using spatially dispersed thermosensors at 16 prostatic sites. The patients were evaluated 5 to 12 days postoperatively with MRI of the prostate utilizing a pelvic phased-array coil at 1.5 T.
Results: Postprocedure MRI demonstrated a mean perfusion defect of 28.1+/-2.1% and 63.6+/-34% of the total gland and transition zone volumes, respectively. The mean anteroposterior (AP) and transverse diameters of the perfusion defects, as measured on the MRI images, were 29.2+/-5.2 mm and 32.7+/-5.9 mm, respectively. The maximum mean peak temperatures were 66.8+/-13 degrees C and were recorded at 4 mm from the urethra. No temperatures higher than 45 degrees C were recorded beyond 15 mm on either side of the urethra in the AP direction and beyond 16 mm on either side of the urethra in the transverse diameter. This perfusion defect was persistent for 27.7+/-5.2 mm in the superoinferior diameter, which is equivalent to the length of the antenna (28 mm).
Conclusion: Perfusion defect diameters as measured by postprocedure MRI accurately represent the prostatic tissues exposed to temperatures of > or =45 degrees C for 45 minutes or more. So, MRI provides an accurate, noninvasive method for screening the effective heat pattern generated in the prostate during transurethral microwave thermotherapy.