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.