Transurethral microwave hyperthermia for benign prostatic hyperplasia: the Leuven clinical experience

Helical antenna arrays for interstitial microwave thermal therapy for prostate cancer: tissue phantom testing and simulations for treatment

Interstitial microwave therapy is an experimental treatment for prostate cancer. The objective of this work was to measure the power deposition (specific absorption rate, SAR) patterns of helical microwave antennae both individually and in array patterns that would be useful for clinical treatment protocols. Commercial helical antenna 3D SAR patterns were measured in muscle equivalent phantoms using a thermographic technique. Two array patterns were tested: a 'square' and a 'crescent' array, both surrounding the urethra. To assess the feasibility of pre-treatment planning, the measured SAR patterns were input to a treatment planning computer simulation program based on a series of trans-rectal ultrasound images from a prostate cancer patient. The simulation solved the Pennes linear bioheat heat transfer equation in prostate tissue, with the aim of achieving a target of 55 degrees C at the prostate periphery while not allowing normal surrounding tissues (bladder, urethra, rectum) to rise above 42 C. These criteria could not be met with the square array but they could be met with the crescent array, provided that the prostate was first dissected away from the rectum. This can be done with a procedure such as 'hydrodissection', where sterile saline is injected to separate the prostate and rectum. The results of these SAR measurements and heat transfer simulations indicate that arrays of helical antennae could be used for safe and effective thermal therapy for prostate cancer.

Evaluation of the effectiveness of transurethral radio frequency hyperthermia in the canine prostate: temperature distribution analysis

The heating pattern of a transurethral radio frequency (RF) applicator and its induced steady-state temperature field in the prostate during transurethral hyperthermia treatment were investigated in this study. The specific absorption rate (SAR) of the electromagnetic energy was first quantified in a tissue-equivalent gel phantom. It was used in conjunction with the Pennes bioheat transfer equation to model the steady-state temperature field in prostate during the treatment. Theoretical predictions were compared to in vivo temperature measurements in the canine prostate and good agreement was found to validate the model. The prostatic tissue temperature rise and its relation to the effect of blood perfusion were analyzed. Blood perfusion is found to be an important factor for removal of heat especially at the higher RF heating level. To achieve a temperature above 44 degrees C within 10 percent of the prostatic tissue volume, the minimum RF power required ranges from 5.5 W to 36.4 W depending on the local blood perfusion rate (omega = 0.2-1.5 ml/gm/min). The corresponding histological results from the treatment suggest that to obtain better treatment results, either higher RF power level or longer treatment time (> 180 minutes) is necessary. This is consistent with the predictions from the theoretical model developed in this study.

Sexual function before and after transurethral microwave thermotherapy for benign prostatic hyperplasia

The effect of transurethral microwave thermotherapy (TUMT) for benign prostatic hyperplasia (BPH) on the ability of achieving erection and ejaculation was studied in one hundred and twenty patients. The patients underwent a single TUMT session for one hour without complementary treatment during the follow-up period of one year. A self-administered questionnaire on sexual functions was used. Our results showed that, despite individual reductions, there was an overall improvement in the ability to achieve erection. It was concluded that TUMT did not have any major adverse effects on sexual functions. However, it was not possible to predict that TUMT will improve sexual functions for the individual patient. Improvement of symptoms and a better quality of life may influence the results.

Temperature-correlated histopathologic changes following microwave thermoablation of obstructive tissue in patients with benign prostatic hyperplasia

OBJECTIVES

To determine the intraprostatic pathologic changes following accurately measured doses of transurethral microwave thermal energy in patients with benign prostatic hyperplasia.

METHODS

Eight patients scheduled for prostate surgery were treated for approximately 1 hour without anesthesia using a newly designed microwave treatment catheter that allows a close impedance match to prostate tissue and concentrates thermal energy preferentially in the anterior and lateral prostate gland. Interstitial, urethral, and rectal temperatures were continuously measured using a novel stereotactic thermal mapping technique. Serial sections of prostate tissue harvested during subsequent surgery were evaluated pathologically with prostate mapping.

RESULTS

Microwave treatment resulted in marked and continuous intraprostate temperature elevation, while urethral and rectal temperatures remained low. Peak intraprostate temperatures in individual patients reached as high as 80 degrees C. Mean temperature reached a maximum of 54 degrees C at a radial distance of approximately 0.5 cm from the urethra and remained 45 degrees C or higher up to a distance of 1.6 cm. The predominant pathologic findings were uniform hemorrhagic necrosis and tissue devitalization without significant inflammation. The mean distance from the urethra to the viable-necrotic tissue border was 1.6 +/- 0.2 cm (range, 0.5 to 2.5). At this border, no more than 1 mm in thickness, temperature averaged 45.7 +/- 0.6 degrees C, and there was a suggestion that pure stromal nodules were more resistant to thermal injury.

CONCLUSIONS

Microwave treatment can destroy obstructive prostate tissue while maintaining innocuous urethral and rectal temperatures. Temperatures of 45 degrees C or higher for approximately 1 hour cause uniform thermoablation of prostate tissue.

Responders and non-responders to treatment of benign prostatic hyperplasia with transurethral microwave thermotherapy

One hundred and seventy two patients with benign prostatic hyperplasia (BPH) were treated with transurethral microwave thermotherapy (TUMT) using Prostcare (Bruker Spectrospin). The treatment was performed with an effect of 52 W and a frequency of 915 MHz, which was generally well tolerated and no serious side effects were observed. In the majority of the patients there was an improvement of subjective symptoms with a significant decrease in Madsen and bothering scores after treatment. In the total patient group, Qmax and voided urine volume were increased slightly, but not statistically significantly. The patients were divided in responders and non-responders, based on Madsen symptom score after 3 months or if complementary treatments were necessary during the follow up period of one year. No significant differences between the groups were observed regarding pretreatment variables except that patients in the responder group experienced the treatment more painful than non-responders. Qmax in the responder group was significantly improved at 6 and 12 months follow up. PSA levels increased significantly after the treatment. Routine evaluation using flow rate, estimation of prostatic size, measurement of residual urine volume and cystoscopy does not give sufficient information for predicting treatment outcome.

Cooled microwave transrectal applicator with adjustable directional beam for prostate treatment

A new intracavitary applicator design for microwave hyperthermia, particularly for transrectal prostate treatment, is presented. It includes an exchangeable multisection antenna that enables us to create a required longitudinal heating pattern, a cooling system to shift the maximum temperature away from the surface and a microwave reflecting system embedded in the cooling system that allows one to shape the irradiation beam in a transverse direction. Independent control of the longitudinal and transverse irradiation patterns of the applicator along with the cooling system, enable precise heating of selected tissues. Results of SAR measurements, E-field measurements and steady state temperature distributions, in solid and liquid tissue-equivalent phantoms are presented. Clinical performance of this applicator was evaluated earlier in patients heated intraoperatively and in a phase I clinical study. The applicator was found capable of effectively heating a tissue volume extending radially 3-25 mm from the applicator surface, angularly defined by configuration of reflecting system and longitudinally determined by specific choice of the multisection antenna.