Aspects on transurethral microwave thermotherapy of benign prostatic hyperplasia.

The underlying principle behind new minimal invasive procedures, such as microwave thermotherapy, is to coagulate the prostatic adenomatous tissue by means of heat. This article describes the action of heat on tissue and identifies areas of concern during treatment. The extent of the necrosis during treatment is governed by two physical variables: the intraprostatic temperature and the duration of the heat exposure. The prostatic blood flow is a key factor for the outcome of microwave treatment because it acts as a coolant and may effectively sink the temperature in the treatment area. Blood flow can vary substantially between patients and may change significantly during treatment. By measuring the intraprostatic temperature and varying the microwave power accordingly, it is possible to compensate for the large variations in prostatic blood flow and obtain consistent treatment.

Cell-kill modeling of microwave thermotherapy for treatment of benign prostatic hyperplasia.

PURPOSE: We investigated whether cell-kill modelling could be used as a mean for predicting the outcome of microwave thermotherapy for benign prostate hyperplasia (BPH). METHODS: The two models--Henriques' damage integral and Jung's compartment model--were implemented in a computer program. Real treatment data for 22 patients with BPH who were in chronic retention were used as input, including measured intraprostatic temperatures and microwave power. To test if modelling gives results that are consistent with actual observations, comparison with transrectal ultrasound (TRUS) measurements of the prostate volume before and after treatment was made. The sensitivity of the computer model for variations in the heat cytotoxicity and the temperature probe location in the adenoma was also tested. RESULTS: The average TRUS volume reduction 3 months after treatment was 26 cc, whereas the corresponding cell kill calculation was 27 cc. The computer model appears to be rather insensitive to minor uncertainties in heat sensitivity and location of the intraprostatic reference temperature sensors. CONCLUSION: Cell-kill modelling appears to give results that are consistent with actual observations. The coagulated tissue volume is calculated in real time during the treatment, thereby providing an immediate prediction of the treatment outcome. By using cell-kill modelling, the endpoint of a treatment can be set individually; e.g., when a certain volume reduction has been achieved.

Clinical results of microwave thermotherapy for benign prostatic hyperplasia.

Transurethral microwave thermotherapy is a truly office procedure without the need for anesthesia for the treatment of lower urinary tract symptoms caused by benign prostatic hyperplasia. Several devices have been developed. Continuous refinement of the procedure led to higher energy protocols and high-intensity dose protocols applying the heat-shock strategy. We report on the clinical results of these protocols. Symptom scores improve around 60%, whereas maximum urinary flow rate improve from an average 9 to 10 mL/sec at baseline to 14 to 15 mL/sec during follow-up. No significant differences have been shown between the outcomes with the different devices. Long-term data show satisfactory results after 4 years. Initial clinical results with the heat-shock strategy show results comparable to those of higher-energy protocols with decreased morbidity. Treatment morbidity of higher energy protocols is moderate and consists mainly of the need for catheterization and a higher percentage of retrograde ejaculation. To improve treatment efficacy, patient selection appears to be most important. Prostate size, bladder outlet obstruction, age, and prostate composition are of predictive value for treatment outcome. Further development of the treatment protocols and refinement of the urethral applicators might enhance outcome.

New technologies for the surgical management of symptomatic benign prostatic enlargement: tolerability and morbidity of high energy transurethral microwave thermotherapy.

High-energy transurethral microwave thermotherapy is an attractive alternative outpatient single-session treatment for symptomatic benign prostatic enlargement, with good tolerability, low morbidity and few complications. This paper reviews recent published literature, with a focus on tolerability and morbidity.

Optimizing transurethral microwave thermotherapy: a model for studying power, blood flow, temperature variations and tissue destruction.

OBJECTIVE: To examine the role of microwave power and blood flow on temperature variations and tissue destruction in the prostate, using a theoretical model of transurethral microwave thermotherapy (TUMT), and thus compare fixed-energy TUMT with no intraprostatic temperature monitoring (constant microwave power applied over a fixed period) with 'feedback' TUMT in which the microwave power is adjusted according to the monitored intraprostatic temperature. MATERIALS AND METHODS: The temperature distribution in the prostate was modelled for a typical TUMT catheter at various blood flow rates. The volume of tissue destroyed was simultaneously calculated from cell survival data after thermal exposure. The calculated quantity of tissue destroyed at the different microwave power levels and blood flow rates was used to describe qualitatively the simulated treatments. RESULTS: Treatment monitoring and consistency were better during feedback TUMT than fixed-energy TUMT, in that the former compensated for variations in blood flow rate. The modelled values agreed with observations during real TUMT. CONCLUSIONS: Blood flow rate is a key factor in the outcome of TUMT. Only by measuring intraprostatic temperature is it possible to compensate for the large variations in prostatic blood flow and obtain consistent treatment results. Repeated interruptions prompted by high rectal temperatures should be minimized and preferably avoided, as the quantity of tissue destroyed is then greatly reduced, and in extreme cases the treatment is totally ineffective.

Intraprostatic temperature monitoring during transurethral microwave thermotherapy for the treatment of benign prostatic hyperplasia.

PURPOSE: We evaluated whether the results of transurethral microwave thermotherapy improve using high intraprostatic temperatures of 55C or greater. MATERIALS AND METHODS: We accrued 30 men 58 to 85 years old (mean age 69) from the waiting list for transurethral prostatic resection in whom maximum urinary flow was less than 13 ml. per second and Madsen score was greater than 8. According to the Abrams-Griffith nomogram all but 1 patient had obstruction. Before treatment 3 thin temperature probes, each containing 5 sensors in a row, were introduced into the prostate from the perineum and positioned using transurethral ultrasound guidance. The microwave power of the transurethral microwave thermotherapy equipment was set based on the actual temperature in the prostatic tissue. A temperature of at least 55C and often more than 60C was reached at the hottest spot. Treatment duration was 1 hour. Postoperatively an indwelling catheter remained in place for 2 weeks. Patients were followed for 6 months with the first followup after 3 months. RESULTS: At the 3-month followup mean maximum urinary flow had increased from 7.4 to 12.5 ml. per second and the mean Madsen score had decreased from 12.6 to 2.9. At the 6-month followup mean maximum urinary flow was 12.2 ml. per second and the mean Madsen score was 3.4. Using pressure-flow data we divided the patients into responders and nonresponders. In the 18 responders maximum urinary flow had increased from 7.2 to 14.6 ml. per second (103%), the Madsen score had decreased from 12.5 to 1.4 (89%) and detrusor pressure had decreased from 9.2 to 6 kPa. (35%). CONCLUSIONS: High energy transurethral microwave thermotherapy relieved bladder outlet obstruction in 60% of the patients and had a good effect on symptoms. Compared with a previous multicenter study with 40% responders, using the same criteria there were 60% responders in our series. Our results indicate that better control of intraprostatic temperature provides better results, approaching those after transurethral prostatic resection.

The heat is on--but how? A comparison of TUMT devices.

OBJECTIVE: To compare the heat characteristics of the microwave antennae, the absorbed energy in the target volume and the cooling capacity of the catheters of three common devices for transurethral microwave thermotherapy (TUMT), i.e. the Prostcare, Prostatron and ProstaLund. MATERIALS AND METHODS: The microwave emission from the respective catheters or antennae was measured in a tissue-equivalent 'phantom' prostate. From these measurements the distribution of absorbed energy from the respective catheters and antennae was calculated from the characteristics of the phantom, the absorbed energy and the temperature difference before and after heating. The cooling capacity of the different catheters were measured by submerging each catheter in a thermally isolated water bath at a known temperature and determining the cooling of the water bath caused by the catheter. RESULTS: The design of the microwave antenna influenced the heating profile significantly. The energy absorbed by the prostate model varied among the devices, but was between 13 and 21% of the stated applied energy. The cooling capacity also varied, being least in the Prostcare and greatest in the ProstaLund catheters. CONCLUSIONS: Users of TUMT should be aware of possible back-heating along the catheter, as this limits the microwave power that can be used safely. Furthermore, the 'treatment energy', which is commonly used as an indicator to describe the intensity of TUMT treatments, is ambiguous and not stringent, in that the microwave energy absorbed in the prostate is only a small fraction of this value.