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

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.

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.

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.

Coretherm microwave treatment causes significant tissue necrosis of the prostate, bladder neck and urethral mucosa. The cell kill calculation provides an on-line estimate of the amount of necrosis caused during treatment.