A comparison of transurethral and transrectal microwave hyperthermia in poor surgical risk benign prostatic hyperplasia patients

Office-based transurethral microwave thermotherapy using the TherMatrx TMx-2000

BACKGROUND AND PURPOSE

Transurethral microwave thermotherapy (TUMT) is an effective therapy for symptomatic benign prostatic hyperplasia (BPH), but the trade-off between the magnitude of clinical improvement and side effects and patient tolerance has limited its appeal to patients and urologists. This study, using the TherMatrx TMx-2000, a TUMT device that directly heats the transition zone to greater than 50 degrees C, has been focused on resolving these issues and developing a truly office-based therapy that is well tolerated with a benign post-treatment course.

PATIENTS AND METHODS

This study was multi-institutional and designed as a blinded, randomized, and sham-controlled trial. A series of 200 patients with an AUA Symptom Index (AUASI) of >12, a peak flow rate of <12 mL/sec, and cystoscopic evidence of BPH were randomized 2:1 (active to sham) and treated in seven physician offices under a Food and Drug Administration-supervised and audited premarket approval protocol. No intravenous sedation was used in any patient. Follow-up for the sham-treatment group was 3 months, at which time, patients could cross over to an active treatment. A total of 119 patients have completed 1-year follow-up.

RESULTS

The active and sham groups were statistically identical at baseline. The 1-hour total treatment was extremely well tolerated using urethral lidocaine and oral medications; not a single prostate block or parental dose of medication was required. The active-treatment group demonstrated a statistically significant reduction (p < 0.05) in AUASI at 3 months compared with sham treatment, with an AUASI decrease from 22.4 to 12.4 (n = 124) for active v 22.9 to 17 for sham (n = 62). For the 119 patients in the active arm who have reached 12 months, the AUASI has fallen to 10.6 points (47.1% decrease), and the peak flow rate has increased 5.0 mL/sec (58.1%). Postprocedure catheterization was typically 2 or 3 days, and the 16.8% of patients who failed their first voiding trial all voided within 1 week. No major adverse events such as stricture, rectal findings, or ejaculatory changes have been reported.

CONCLUSIONS

This study demonstrates that the TherMatrx TMx-2000 TUMT effectively treats symptomatic BPH in the physician office with minimal morbidity.

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.

Does transurethral microwave thermotherapy have a different effect on prostate cancer than on benign or hyperplastic tissue?

OBJECTIVES

Transurethral microwave thermotherapy is useful for the treatment of benign prostatic hyperplasia, but its effect on cancer is not documented. We analyzed the pathologic changes occurring after microwave thermotherapy in whole mount radical prostatectomy specimens from patients with cancer.

METHODS

Nine patients scheduled for radical prostatectomy for clinically localized prostate cancer were treated with transurethral microwave thermotherapy (Urologix Targis System). Patients ranged in age from 64 to 72 years (mean 68). Seven patients underwent prostatectomy 4 to 90 hours after thermotherapy, and 2 other patients underwent prostatectomy 12 months after thermotherapy. Whole mount totally embedded prostates were mapped for necrosis and cancer, and the volume of each was measured by the grid method.

RESULTS

Pathologic stages were T2a (n = 4), T2b (n = 4), and T3b (n = 1). The prostates from patients who underwent radical prostatectomy within 4 to 90 hours of thermotherapy had a mean prostate weight of 47.4 g (range 19.5 to 70.3). Each consistently showed hemorrhagic necrosis and tissue devitalization without significant inflammation. Necrosis involved contiguous areas of benign epithelium, stroma, and cancer without skip areas. The mean volume of necrosis was 8.8 cc (range 1.4 to 17.8), and the mean percentage of the prostate involved by necrosis was 22% (range 3% to 39%). The necrosis was symmetric around the urethra in 6 of 7 cases. Urethral dilation was observed in 3 patients, and the mean maximum radial distance of necrotic tissue was 1.4 cm (range 0.6 to 1.8). Necrotic change was noted in 80% to 100% of the volume of cancer in 4 cases, 40% to 60% in 2 cases, and 5% in 1 case. The prostates from the 2 patients who underwent radical prostatectomy 12 months after thermotherapy had a mean weight of 88 g (55 and 121 g, respectively). Each showed periurethral fibrosis, nonspecific chronic inflammation, and squamous metaplasia of the urothelium. The mean volume of necrosis remaining was 0.2 cc. The mean percentage of the prostate involved by necrosis 1 year after thermotherapy was less than 1%. There was some reabsorption of dead tissue. The mean maximum radial distance of the necrotic tissue was 0.4 cm (0.2 and 0.7 cm, respectively). The prostatic urethra had viable and partially denuded urothelium in all cases.

CONCLUSIONS

Microwave thermotherapy is clinically useful for ablation of benign prostate and cancer contiguous to the urethra, resulting in hemorrhagic necrosis with minimal damage to the urethra. There was no apparent differential morphologic sensitivity of benign prostatic tissue, hyperplastic tissue, or cancer to thermotherapy.

Microwave thermotherapy: a long-term follow-up of 67 patients from a single centre

OBJECTIVE

To determine the long-term therapeutic value of transurethral microwave thermotherapy (TUMT) in the treatment of bladder outflow obstruction secondary to benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

A total of 67 patients with BPH, assessed using symptom scores and measurements of urinary flow rate, underwent TUMT using the Leo Microthermer system (Laser Electro Optics Ltd, London, UK) between October 1990 and June 1992. Follow-up information was obtained on 60 patients (90%). If they had undergone no further treatment for their BPH, they were re-assessed with symptom scores and measurements of flow rate.

RESULTS

The mean follow-up was 52.4 months; eight of the 6 7 patients had died and seven were lost to follow-up. Sixteen of the remaining 52 (31%) had undergone another treatment for BPH; one patient developed prostatitis and one developed localized carcinoma of the prostate. Thirty-four patients had had no further treatment, 29 of whom attended for assessment. In these patients, a statistically significant improvement in both the symptom score and flow rate was maintained at 4 years. No patients developed retrograde ejaculation.

CONCLUSION

This is the first study to report a follow-up of at least 4 years after TUMT with any device. Treatment with the Leo Microthermer provided at least a 50% symptomatic improvement in 16 of 50 patients treated at 4 years. However, 30% of the patients needed further treatment for their BPH. TUMT is safe and effective in patients not wanting anaesthesia and in young patients concerned about retrograde ejaculation.

Transurethral balloon laser thermotherapy for urinary retention in patients with benign prostatic hyperplasia who are at high surgical risk

BACKGROUND

Twelve patients with benign prostatic hyperplasia and urinary retention, who were considered to be poor candidates for prostatectomy, were treated by transurethral balloon laser thermotherapy (TUBAL-T). The mean patient age was 78.9 years (range, 66 to 93 years) and the mean duration of bladder catheterization was 11 weeks (range, 2 to 48 weeks).

METHODS

Irradiation into the prostatic tissue was done through 360 degrees with a neodymium: yttrium aluminum garnet (Nd:YAG) laser balloon placed in the prostatic urethra, with pain relief provided by using local topical anesthesia. The total laser dose was from 45,000 to 123,376 J, with an average of 73,089 J. The irradiation time was from 40 to 54 minutes, with an average of 45.2 minutes.

RESULTS

Spontaneous voiding became possible in all patients at a mean of 2.8 days (range, 1 to 7 days) after irradiation. The mean catheter-free period was 20.5 months (range, 6 to 34 months), with the longest being 34 months. The international prostatic symptom scores, quality-of-life scores, and peak uroflow rates showed substantial improvement after laser thermotherapy. To date, long-term resumption of spontaneous voiding was successfully achieved in 9 of 12 cases (75%).

CONCLUSION

TUBAL-T is safe and effective alternative for treatment of urinary retention in patients with benign prostatic hyperplasia who are considered to be at high surgical risk.

Transurethral thermotherapy in the management of benign prostatic hyperplasia

Transurethral radiofrequency thermotherapy for symptomatic benign prostatic hyperplasia was performed in 50 selected patients, using the THERMEX II device. High surgical risk patients were included, among them 13 previously catheterized ones, because of unresolved retention for more than 6 months. The treatment consisted of a three-hour single session at 47 degrees C. Follow-up studies were carried out at 1, 3, 6 and 12 months using Madsen score, maximum flow rate, residual urine volume determinations and prostate bulk measurement by transrectal ultrasound. Subjective and objective improvement (of more than two parameters) was noticed in 62% of the patients. Prostatic volume did not change. In the retention group 54% of the patients remained free of catheter. Postoperative histology in 8 cases that failed to respond, revealed focal haemorrhagic and necrotic changes in periurethral glandular tissue. This is a promising method for selected high risk patients that achieves reasonable but not comparable results to TURP and requires further investigation in larger patient groups with BPH.

Transurethral microwave thermal therapy: pathologic findings in the canine prostate

Microwave irradiation administered by transurethral transducer to the prostate permits focused hyperthermia with resultant tissue ablation; a coding system within the catheter allows urethral preservation. We evaluated the effect of microwave hyperthermia in 13 dogs receiving 48-79 min of focused irradiation (16-45 watts, intraprostatic temperature > 45 degrees C) delivered by a specially-designed transducer with an operator-controlled directional antenna (T3, Urologix Inc., Minneapolis, MN); one other dog had transducer placement without irradiation (sham control). After treatment, the dogs were in good health, voiding well without complications, and were sacrificed after 5-38 days. The prostate and vasa deferentia were removed, fixed in 10% formalin, grossly inspected, cut at 5 mm intervals, and serially sectioned with whole mount sections; representative sections of the adjacent rectum and distal bladder were also obtained. All cases were histologically evaluated with prostatic mapping without knowledge of treatment or time of sacrifice. In the acute phase (5-13 days), the prostate showed sharply circumscribed periurethral coagulative necrosis with hemorrhage; necrosis was also seen in the mucosa and bladder wall of those with transducers placed at the bladder neck. In the subacute phase (17 days), the hemorrhagic necrosis was resolving, often with cystically dilated urethra due to sloughed necrotic tissue; the urothelium was intact. By 24-38 days, the necrosis was in the late stages of resolution, with residual patchy acute and chronic inflammation at the periphery, and frequent persistence of megalourethra. In all cases, the prostatic capsule was intact, the urethral mucosa was preserved, and the vasa deferentia and rectum were normal except for two cases with mild fat necrosis. Microwave irradiation allows precisely localized thermal ablation of prostatic tissue and enlargement of the urethral bore without clinical complications in dogs, offering promise as a therapeutic alternative to surgery in select patients with symptomatic prostatic nodular hyperplasia.

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.

A sham controlled trial of transurethral microwave therapy with subsequent treatment of the control group

To investigate whether there is a significant placebo component to the improvements seen after 1-session transurethral microwave treatment, 40 patients with significant symptoms of prostatism and unequivocally benign glands were recruited to take part in a sham controlled study. After an active treatment the mean American Urological Association symptom scores improved by 63% (19.2 to 7.1) while after a sham treatment symptom scores improved only marginally (18.8 to 16.2, p < 0.001). Residual volumes decreased by 50% (104 to 52 ml.) and flow rates increased by 2.3 ml. per second after an active treatment with no improvement after a sham treatment. There was a consistently greater improvement after an active treatment compared to a sham treatment. Patients who had received a sham treatment were then offered an active treatment and showed improvements similar to those in the original actively treated group and much greater than after the original sham treatment. Mean symptom scores decreased from 16.2 to 9.9 (p < 0.004). Residual volumes decreased from 94 to 40 ml. (p < 0.005) and flow rates increased by 1.6 ml. per second, while these same criteria had deteriorated after a sham treatment. Side effects were mild and short lived, with no patients reporting sexual dysfunction as a consequence of treatment. Transurethral microwave therapy is an effective well tolerated treatment for select patients with benign prostatic hypertrophy and the placebo effect of treatment is minimal.

Optimization of transurethral hyperthermia: number of treatments

OBJECTIVE

The optimal number of transurethral microwave hyperthermia (TUHT) treatments in patients with moderate to severe symptoms of benign prostatic hyperplasia (BPH) is not known. This study was designed to compare TUHT efficacy with the use of three versus six treatments.

METHODS

In a Phase II prospective trial during a three-month period, 28 poor surgical risk patients with moderate to severe prostatism were randomized to receive three or six TUHT sessions. TUHT treatments were given on an outpatient basis without sedation or anesthesia for sixty minutes at 915 MHz with the temperature controlled on the urethral surface at 45 degrees C.

RESULTS

Subjective improvement was obtained in 7 (50%) patients receiving three TUHT treatments and in 12 (86%) patients receiving six treatments. A greater degree of improvement in total symptom score (P = 0.01) and obstructive (P = 0.01) and irritative (P = 0.04) symptoms was also recorded in the 14 patients receiving six treatments compared to those treated with three TUHT sessions (P = 0.01). A posttreatment improvement in objective study parameters was recorded for both treatment groups. The 14 patients treated with six TUHT sessions, however, showed a better improvement in peak flow rates (51% vs. 8.4%, P = 0.003) and postvoiding residual volume compared to the 14 patients treated with three TUHT sessions (P = 0.10). Treatments were very well tolerated and no clinically significant toxicity was recorded. Of the 9 study patients who failed to respond to treatment, 1 patient was successfully retreated with TURP while 8 patients required an indwelling catheter.

CONCLUSIONS

In TUHT in poor surgical risk patients with BPH with the temperature controlled at 45 degrees C, six treatments were superior to three treatments, based on a higher incidence of subjective and objective improvement.

Transurethral microwave thermotherapy for uncomplicated benign prostatic hyperplasia. A prospective study with emphasis on symptomatic improvement and complications

A single session of transurethral microwave thermotherapy (TUMT) was used in 115 patients with symptomatic uncomplicated benign prostatic hyperplasia (BPH). Subjective symptoms and urodynamic parameters were assessed before treatment, at 6 weeks, 3, 6 and 12 months after treatment and complications recorded. There was significant improvement in obstructive, irritative and total symptom scores at all time intervals. The maximum and corrected flow rate improved significantly at all time intervals as well as the decrease in residual urine. Complications occurred in 45.2% patients with no mortality. The most frequent complications were urinary tract infection (32.1%) and urinary retention (28.6%). Two patients experienced retrograde ejaculation. No patient was hospitalized due to complication. Four (3.5%) patients required transurethral resection of the prostate during the follow-up period due to persistent symptoms; 96.5% have remained satisfied. In conclusion, TUMT is a promising treatment option in selected patients with BPH, is well tolerated and complications are easy to treat. Its main advantage is the fact that it can be administered on an outpatient basis, thus reducing patient inconvenience and costs.

Hyperthermia as a treatment modality in benign prostatic hyperplasia

OBJECTIVE

To review the current status of hyperthermia (heating the prostate up to 45 degrees C) as a treatment modality for benign prostatic hyperplasia (BPH).

METHODS

Hyperthermia versus thermotherapy is defined, the techniques and equipment are presented, and the current English literature regarding safety and efficacy is reviewed.

RESULTS

Both transrectal and transurethral heat applications are very safe procedures. Most studies evaluating the efficacy have been nonrandomized and uncontrolled. The 50-70 percent symptom improvement rate should be compared with the natural history of the disease and the considerable placebo effect. The few controlled studies produced contradictory results.

CONCLUSIONS

At the present time, hyperthermia has not been shown, in scientifically well-designed studies, to be a treatment modality with measurable and durable outcome in BPH.

A comparison of transrectal hyperthermia, transurethral thermotherapy, urolume wallstent, and prostatic spiral for benign prostatic hyperplasia patients at poor operative risk

Transrectal hyperthermia, transurethral thermotherapy, prostatic stent, and prostatic spiral were used to treat 120 poor operative risk patients with symptomatic benign prostatic hyperplasia. The preoperative subjective and objective conditions of the four groups (each of 30 patients) were comparable. None of the patients had an indwelling catheter, but according to flow nomograms, all were obstructed. The greatest increase in peak flow rate was observed after stent placement, while the greatest decrease of residual urine volume was seen after the insertion of the stent and transrectal hyperthermia. According to maximum flow nomograms, only the placement of the stent resolved bladder outlet obstruction. The greatest improvement in subjective symptoms was the result of stent insertion, but the heating procedures also caused a significant reduction of symptom scores. The spiral produced satisfactory results only in the short term.

Transrectal hyperthermia as palliative treatment for advanced adenocarcinoma of prostate and studies of cell-mediated immunity

During a fifteen-month period, 15 patients with progressive adenocarcinoma of the prostate (CaP) were treated with transrectal microwave hyperthermia (TRHT). There were 5 Stage T4 and 11 Stage T3 patients including 6 patients with skeletal metastases. Nine of the patients had severe and 6 had moderately severe signs and symptoms of CaP. TRHT was given six times at 2,450 MHz with temperature controlled at 43.5 degrees for thirty minutes. Cell-mediated immunity tests were performed before TRHT and at two, four, and six months post-therapy. The results of these tests were compared with those of 15 patients with benign prostatic hyperplasia (BPH) treated with the same TRHT and with 30 untreated normal volunteers. TRHT was well tolerated with mild acute toxicity noted in 3 patients (20%). Of the 15 patients treated, 2 (13%) showed scintigraphic evidence of regression of bone metastases. Five patients survived more than five years since treatment, and in 3 patients there was no evidence of CaP. A decrease of marked or moderate degree in signs and symptoms of CaP was noted in 8 patients (53%). The results of cell-mediated immunity tests were of interest. The 15 CaP patients prior to TRHT had lower OKT4/OKT8 ratio, lower PHA transformation index, and lower Con-A induced T-cell suppressor activity as compared with the 15 BPH patients and 30 healthy volunteers, who had normal immune parameters (p < 0.01). Following TRHT there was a significant increase in the monitored immune parameters noted in the 15 CaP patients (p < 0.01). This immune stimulation peaked at two months and gradually decreased to near pretreatment levels at six months. In the 15 BPH patients post-TRHT changes in immune tests were less apparent. The results of this small study, if confirmed, could be of clinical importance in patients with advanced prostate cancer.

Transurethral microwave treatment for benign prostatic hypertrophy: a randomised controlled clinical trial

OBJECTIVES

To determine whether transurethral microwave treatment for patients with benign prostatic hypertrophy provides significant symptomatic relief, a reduction in residual urine volumes, and improvements in flow rates compared with sham treatment.

DESIGN

Prospective double blind randomised study with follow up at three months.

SETTING

Department of Urology in a London teaching hospital.

PATIENTS

40 men completed the study: 22 received microwave treatment and 18 received sham treatment. Entry criteria were symptoms of prostatism of at least six months' duration, a total symptom score > 14, and a peak urine flow rate < 15 ml/s or a residual urine volume > 50 ml. Exclusion criteria were prostatic cancer, a residual urine volume > 200 ml, a very large prostate, an obstructing middle lobe, acute urinary retention, impaired renal function, coexisting urinary tract disease, and previous prostatic surgery.

INTERVENTIONS

A single 90 minute transurethral microwave treatment or sham treatment.

OUTCOME MEASURES

Patients' symptoms (including daytime frequency and nocturia) recorded in a self assessment symptom score questionnaire, peak urinary flow rates, and residual urine volumes.

RESULTS

The mean total symptom scores of the patients who received microwave treatment fell from 30 to 11 compared with a fall from 31 to 26 for patients who received sham treatment (p < 0.001). Among patients who received microwave treatment daytime frequency fell from 9.4 to 5.5 voids a day and night time frequency from 3.5 to 1.6 voids a night; residual urine volumes fell from 104 ml to 52 ml; and peak urine flow rates increased by 2.3 ml/s. In the control group there was no improvement in any of these features. Treatment preserved sexual function and antegrade ejaculation.

CONCLUSIONS

For selected patients with prostatism microwave treatment is effective and has few side effects.

Temperature steering in prostate by simultaneous transurethral and transrectal hyperthermia

Localized hyperthermia (HT) is presently under investigation as a treatment for benign prostatic hyperplasia and carcinoma of the prostate (CaP). One popular approach employs a transrectal (TR) device, a directional microwave (MW) applicator inserted into the rectum and aimed at the prostate. Alternatively, in the transurethral (TU) technique, a symmetrically radiating MW antenna is placed directly within the prostatic urethra. Used individually, TR applicators are capable of effectively heating (> 42 degrees C) the prostate up to 2 cm from the rectum, whereas TU applicators selectively heat the periurethral tissue with effective radial penetration of about 0.6 cm. Neither technique is of much value in heating the anterior prostate. In general, the highest temperatures are produced in the tissue immediately adjacent to the surface of intracavitary microwave devices. However, when MW antennas are used in arrays, the resulting heating pattern can differ significantly from that of the individual antennas. Heating at depth can be selectively enhanced and "steered" by adjusting the phase relationship between the devices. Prostatic temperature profiles were measured in 6 patients treated with TR alone, TU alone, and simultaneous TR and TU heating. In the combined treatments different phase relationships between the antennas were applied. We found that a higher temperature could be produced in the center of the prostate than on the surface of either applicator for certain phase relationships, and that the temperature profiles could be changed by shifting phase. The results of these measurements are in agreement with those of a computer simulation. Based on the above data we feel the combined use of TU and TR hyperthermia may be justified in Phase I-II trials for patients with locally advanced CaP.

Relationship of response to transurethral hyperthermia and prostate volume in BPH patients

A response to transurethral microwave hyperthermia (TUHT) at 915 MHz and its relationship to prostate volume was examined in 63 poor surgical risk benign prostatic hyperplasia (BPH) patients. All patients had moderate-to-severe obstructive signs and symptoms, and received > or = 5 TUHT one-hour sessions. Treatment temperature was controlled on the urethral surface at 45 degrees C +/- 1 degree C. Follow-up ranged from twelve to forty-four months (mean 18 months). The mean prostate volume was 57 cc (range 10-301 cc). There were 40 patients (63%) with prostate volume < or = 50 cc and 23 (37%) with a volume > 50 cc. Treatment failure was seen in 6 patients (10%). It was 10 percent in 40 patients with smaller glands and 9 percent for those 23 with larger prostates, N.S. at p = 0.49. Subjective treatment response was seen in 58 patients (92%). It was 90 percent for the 40 patients with < or = 50 cc prostates vs. 96 percent for the 23 with > 50 cc prostates, N.S. at p = 0.75. This study suggests that the initial prostate volume is not an important parameter predicting response to TUHT.

Transurethral hyperthermia for benign prostatic hyperplasia patients with retention

From 1989 to 1990, 32 poor surgical risk patients with urinary retention were treated with transurethral microwave hyperthermia at the department of urology, University of Leuven in Belgium. Mean patient age was 73 years (range 58 to 90 years) and mean duration of retention was 4 weeks (range 3 to 12 weeks). Followup ranged from 13 to 82 weeks, with a mean of 31 weeks. Bilobar or trilobar hyperplasia was diagnosed in 25 patients (78%), while 7 (22%) had median lobe or median bar hypertrophy. The mean prostatic volume was 52 cc (range 25 to 150 cc). Transurethral microwave hyperthermia was given with a helical antenna at 915 MHz. once or twice per week. The mean number of transurethral microwave hyperthermia sessions was 8.9 (range 5 to 10). Each session consisted of a 60-minute treatment at a mean maximum temperature of 45.4C (range 43.7 to 47.2C), average temperature 43.9C (range 42.7 to 45.5C) and minimum temperature 42.0C (range 40.2 to 43.0C). The temperature was continuously monitored, including thermal mapping in all patients. Of the 25 patients who presented with bilobar or trilobar hyperplasia 18 (72%) were catheter-free for the duration of followup. Of the 7 median lobe or median bar patients 1 (14%) showed sufficient improvement to warrant catheter removal. This patient, however, had recurrent retention 4 months after transurethral microwave hyperthermia. In patients with bilobar and trilobar hyperplasia a strong correlation was observed among maximum temperature (p = 0.0006), average temperature (p = 0.0033) and treatment response. As expected, no such correlation existed between minimum temperature and response to treatment (p = 0.56). Our study has again demonstrated therapeutic activity in patients with benign prostatic hyperplasia treated with transurethral microwave hyperthermia. A new finding was a strong correlation between temperature and response.